Rear Noise "whoop whoop whoop"
 

I just got my first SUV, an 98 explorer 2 door, with the OHV engine and manual transmission, at 80000 miles.

Its making noise, sounds like "whoop whoop whoop whoop..." from around center or rear that goes faster with speed. Not very loud, but quite annoying. The noise seems to be with every 360 degrees tire rotation, and the car seems to "shake" with it a bit. At first I thought its because of the old tires (one of the rear tires was constantly leaking air). So I put new tires on it but the "whoop whoop whoop" remains! The new tire does not shake with the noise anymore though.

Is there something I should be worried about?


Also when I first got it, it was very hard to put into gear, especially 1st and reverse (its a manual). I need to pump the clutch several times to allow it to get into gear. After a couple of days its got much easier, although still need a bit hard sometimes. Is there anything that should be done to this symptom?


Thanks!

It first sounded like you had a bad tire but because the noise is still there but the shake is gone Ihave to think it might be something rubbing the tire or wheel or possibly a wheel bearing.

The clutch problem is that it is likely to be low on brake fluid as it is a hydraulic system or a leak in the system possibly the slave cylinder. Add fluid and pump the clutch and then look for leaks.

Follow the Hayne's Manual for bleeding the clutch, you may need to do it more than once, if you dont have a leak this might help it.

Thanks for your reply!

I just got back from driving around, and I have more information.

The "whoop-whoop-whoop" exist most of the time, more noticeable when driving slower around 30 mph because if I go faster the noise just blend together. However, the intensity actually differs. When depress the clutch pedal when going around 30 mph, the noise become very subtle (but still there). Also the noise will be a bit louder when doing hard acceleration.

Also I said the noise came from the rear. Actually it probably more like center -front (under the shifter).

Bearing? Is it hard to replace bearing? I'm not that experienced with cars especially SUVs but I'm pretty handy with things.

Thanks again!

Pull the rear driveshaft off and check the universals.

I haven't had the chance to drop the driveshaft, maybe when weather gets better a bit. The sound is actually related to power as well. The noise gets stronger when I accelerate, and almost diminishes when I disengage the clutch. But the noise is there always.

Another thing is the engine starts to make rapid clicking/knocking noise beginning about 2800-3000 RPM up. Mostly sound, although i could feel the clicking through the gas pedal and shift stick slightly. Below that RPM the engine stay smooth.

One last thing, I could hear and feel a random "clunk" from under the car, its like the floor hit by a rock or something from time to time. Also there's this probably different kind of clunk that I could not feel with my feet but it happens when I shift, particularly when I fully disengage the clutch.

Thanks for your comments!

I dropped the driveshaft yesterday. The u-joints seem to be ok, smooth movements, the one on the rear is a little bit harder to move but not making any noise. So I changed the rear u-joint anyway, changed with a greasable one.

And... voila... no change, the repetitive whooping sound is still there.

Could it be the differential? or maybe the front u-joint?

The noise become louder during acceleration on speeds above 25 MPH up to about 40 MPH as above that the noise blends with general noise (higher frequency), gone when I release the gas pedal. On speeds between 10 MPH and 25 MPH the noise is always there regardless acceleration/deceleration. Below 10 MPH noise is unnoticeable.

Thanks!

This truck seems to have a multitude of problems, all related to the drive line.
The "clunk" may be an engine or trans mount, the "clicking" felt in the shifter seems to be an internal trans problem and the sound and vibration could be the T/case or even a bent rear axle.
I think you need to take it to a shop with a good rep for diagnosis in your area. Pay them for a thorough diagnosis and then let them fix it or do it your self. If you let them do it. Make sure you get a gauranteed price for the repairs before they start.

Did you check and grease the slip joint while the drive shaft was down?

Would not hurt to check the front drive shaft as it is rotating even when not in 4x.

Have you checked the tires for tread separation?

Yes I would take it to the shop if I have some dough.... darn I'm poor :-banghead

On the slip yoke i put some grease gun on it. When I pulled it out some kind of oil pour out. The slip thing seem to slide in/out smoothly. My explorer is a 2WD so it does not have front drive shaft, no t-case either.

The tires are ok. Tires are new and balanced and aligned.

Take a close look at the axle tubes, where they go into the cast iron housing. Look for a color differential on the tube right at the area closest to the casting. The tubes have been known to shift or slide out a bit from rough usage or even from improper jacking.

the clicking is RPM dependent (happens in any gear). Could that be internal transmission problem? The engine is smooth all the way to about 3000 rpm where it starts to click and the clicks gets louder further up.

I'll check the axles this evening. If the axle tube is bent, what can I do to fix it?

I've been thinking about wheel bearing, but the whoop noise is unchanged during turns. Maybe some other bearings somewhere.

I'm not sure how to properly describe this "whoop" sound, maybe its more like a grind or scrape, like a scraping metal brush.

Thanks everybody for helping me out!

Its been some time until I have the chance to work on my truck again.

I checked the axle tubes. They seem to be ok, no signs of bending.

About the whoop whoop whoop noise (rubbing or scraping noise), the noise has "developed" somehow.
In addition to it getting a bit louder, now the noise is different in relation to acceleration/deceleration. The noise is audible mostly when doing slight acceleration. I tried to save gas so I try to be light with my gas pedal, and this is where the noise is mostly audible. When coasting or hard acceleration, most of the noise is gone, but under 30 MPH the noise stays there regardless of acceleration/coasting. The noise is inaudible below 10 MPH. Also when going slow, around 10-20 MPH, sometimes I can feel the car slightly jerking in relation to the noise. The noise is a cyclic in relation to vehicle speed, and seem to be related to wheel (the noise "whoops" around every wheel rotation).

About noise source, it seems to be more to the front-under than rear. But I may be mistaken.

At some point I was driving and braking, and it felt that the car slightly stutters in relation to the noise. So I started to think its the front brakes or wheel bearings. They are kind of due anyway, so I bought new rotors and pads, and install them. One of the caliper bracket slides on the right side was stuck because of rust, so I sanded it and put it back in with some grease. I also checked the wheel bearings while at it, because with this vehicle the rotor is one with the hub. The bearings seem to be ok, no obvious damage and it made no noise when I rotate the wheel after assembly, but I may be wrong because it may make noise only when weight applied to it.

After all this work however, the noise remains :-banghead

I was thinking it may be the output shaft bearing, but if that is so, the noise should be from right below. And also the driveshaft is rotating faster than the wheel, that means the cycle should be about 3 times the speed of wheel. Is that correct?

Since its coming from the front and its a RWD vehicle, the only thing left to replace is wheel bearing. Although everywhere I read on internet wheel bearing problem does not relate to accelerate/decelerate. Also the noise of wheel bearing problem should be different when I turn, which does not happen to my car.

Any help is appreciated !

Thanks!

The description you have listed "The noise is inaudible below 10 MPH. Also when going slow, around 10-20 MPH, sometimes I can feel the car slightly jerking in relation to the noise. The noise is a cyclic in relation to vehicle speed, and seem to be related to wheel (the noise "whoops" around every wheel rotation). "is exactly what would fit an out of round tire. A tire that is going out of round does so very gradually in most cases, but at high speed the problem accelerates and will often finalize with a blowout. I believe we have been over this ground before but I suggest that you use both hands and feel the circumfrence of the tire most suspect. If you feel any variation as your hands go around the tire, remove it and inspect carefully. You could have a tire that is just beginning to seperate.
Let us know.

Hi, Moto Mel, thanks for replying.

Hmm... I don't think the tire is separating, they are all new only about 2 months old. And also, when I bought new tires (thinking that would solve the problem), the noise was exactly the same before and after replacing tires (with balancing and aligning). Also the jerk is only occassionally felt, especially when climbing, and the car is smooth otherwise.
But not ruling out the possibility that even new tires could separate, I will look closely at this as the noise has developed.

You don't think wheel bearing could be causing this? I'm thinking to just replace them anyway, just 40 dollars for both sides and hope for the best :-bigparty


Oh and about the "clunk" I actually found what caused it when I did the brakes. its the stabilizer mount, the one on the left side is gone (probably rusted out and just broke), so the stabilizer bar was just hanging in there, knocking things.

I checked differential and transmission fluids and they are up to spec. They may not be an indicator of health, just to make sure that its not caused by low fluids.