in my e350, it developed a new noise today. its a howling that only happens above about 30 MPH and only while accelerating. at the throttle position required to maintain 65MPH, its quiet, but any pedal beyond that and i start getting this noise.
now for the things i've checked.
u-joints - had a temp of 98*F when i stopped in a park-n-ride lot to check out my noise
rear diff - had a temp of 113 at that same time
transmission - had a temp of 155 at that same time
wheel bearings - all were cool to the touch at that same time
underhood changes - yesterday i mounted the alternator for my auxilary battery and inverter setup - at the same stop as mentioned above, i removed the belt to it, and the problem remained unchanged.
injectors - on a quick visual inspection there was no sign of fuel leaking out
the noise seems to be coming from behind me, i think - but its a little hard to tell.
the pitch of the noise seems to be affected primarily by engine speed, and its intensity affected by both throttle position and vehicle speed. it happens in both 2nd and 3rd gears

all things considered, the options i see remaining include: sudden change in exhaust noise, driveline issue (but not likely with the low temps there), rear diff setup issue (but not likely with low temps there and no recent changes)
none of those sound like likely options, but i'm not finding much of anything else to look into. any ideas?

 

Is it a real howling sound, or a whine?

 

i might have to say its somewhere between a howl and a whine. i took a video of it from my phone - but its a little hard to hear. you can really hear me getting on and off the pedal here http://dl.dropbox.com/u/39418460/Pic...603_191721.3gp and if it would help i also took one with the image focused on my foot so you can see/hear together when i'm on the pedal and how it adds the noise
listening to the vid from my phone, it almost sounds normal, but that sound is new and quite obnoxious.

 

ok, i studied it a bit more tonight and found a couple points of concern
1) transmission yoke - its a little loose in the tranny. according to my eyecrometer, it has freedom to move vertically about .020 at the seal, and about .100 at the u-joint end of the yoke. for as long as i've owned the truck, its had a wet streak across the underside of the floorboards right around the u-joint, and tonight i noticed a couple drops of ATF hanging from that section of floorboard. the funny thing is that absolutely none of the fluid is on the transmission case, not a single drop.
so i figure i'd better go to town tomorrow and pick up the bushing and seal for that, along with the tailshaft housing gasket, and get to work on it.
2) rear u-joint. it has some slack in it, so i'll be replacing it tomorrow

 

I think I hear that loud sound pretty clearly, my van does the same, but mines from the engine, it only does it in higher RPM's after my dead spot in my throttle.



You hear it so much louder when the air cleaner is off.

 

interesting, john. yours sounds more like it would be an exhaust thing...
but a few funny things about mine make me think its not from the engine itself: doesn't happen below 30mph, regardless of RPM or throttle position. and it started suddenly.
after i take care of the driveline issues in my previous post, i'll come back with the results
thanks--josh

 

so i drove the flatbed to town today and bought both u-joints and the transmission rear seal and bushing, and installed all those parts. both old u-joints showed minor wear (grooving) on the "cross" in the normal way, even though i only noticed slop in the rear one. so i replaced them both, as well as the transmision output shaft seal and bushing, though i found that the new one had almost as much slop as the old one.
with all that done, i took it out for a test drive, and the noise remains. after a few miles of studying it, i decided to try it with the sliding door open, thinking that if it were exhaust noise it would be louder - well it was less noticeable with the door open. then i tried it with the engine cover open by about 4 inches. again, it was less noticeable.
in the process, i also noticed a slight vibration i can feel through the floorboards that appears when the noise is its loudest.
also, i noticed that it starts very quiet as a rythmic noise around 20 MPH, which turns to a howl around 30MPH. makes me think of gears. and this makes me wonder if something may be wrong in my rearend, or possibly my tranny. with this in mind, i checked the fluid in both and found them full. both had the fluid changed less than a year ago
the noise sounds/feels like its to my right, and maybe behind me. with all things considered, i'm guessing either a tranny or a rearend.

for the moment, i'll start wearing earplugs while i drive, as the noise is at a very offensive pitch sometimes, and i might have my local tranny specialist give it a test drive to see what he thinks about it

 

wheel bearing maybe? just a thought anyway. Do any of the wheels have a little slop in them?

 

i just had the feeling it was coming from the diff, so tonight i pulled off the cover and found that i had a broken pinion. i'll plan to baby it for the next couple of days until i can fix it right

 

I was going to suggest look at your pinion bearings, but sounds like you found the problem, albeit still in the rearend.

 

maybe this link will work to show the condition of the pinion as of last night Facebook if not, i'll post it somewhere else and link to it.

my local tranny shop, Snohomish Transmission, will be taking care of this one for me. he found a used gearset and will be installing in on monday

 

My camper has a howling noise from the rear end to, but only happens under load right at 45mph.

Starts around 42mph, loudest at 45 then quiets down and gone by 47mph.


It does make a clunk sound when you shift from R to D or vice versa, but I think it's just to much backlash.


Never took the cover off, probably be a good idea to do that. lol

 

I was going to say the other night to check the rear end, but apparently the site didnt want me making replies so i left it for someone else to offer up. Glad you found it.

 

john, that almost sounds like you might have some driveline noise there - it seems that those often have a chosen speed to make noise, whereas my rearend issue starts where it does and gets louder as i add speed or torque to it.
hairybox, since the noise seemed to be behind me, along with the nature of how it was affected by both speed and torque, that was a thought i had almost from the start, but didn't want it to be true at first. last night i knew i had to open up the cover and see what was there. 2 broken teeth on the pinion. game over.

 

that is kinda like my truck.