I am hoping somebody out there has had a similar problem to me.
98 Expedition, RWD 160k miles
When driving in stop start traffic on a hot day there is this intermittent moaning / whining sound that comes from the front of the car. The sound is not very loud, you can only hear it at a stop. Turning the AC off does not seem to stop the noise, but does seem to reduce the frequency.
Anyway I’ve bought a stethoscope and I’ve listened to the alternator and AC compressor. The problem is that by the time I’ve pulled over and opened the hood the sound seems to go away. FREAK it’s frustrating.
With the stethoscope I’m not really sure what I am listening for, but the alternator sounds healthy (to me). The AC compressor makes a fast clicking sound when it’s on, but its not a “bad” sound.
I read somewhere on here that the bearing on the idler pulley can go bad.
Has anybody had a similar experience to mine? I’d like to fix it now before something goes bad and costs more money to fix.

Thanks
0gers

 

I'v had a similar sound from the front of my Navi, but it only happens when the temperature isless than 20*. The sound seems to be a constant tone, independant of rpm, but if I slip it into neutral and blip the throttle it will stop the moaning.

A few times I have been able to get the hood open before the sound stops. The moaning on my Navi comes from that square box in the intake tract, (the one that is between the MAF and the throttle body). If I put my hand on the box when its moaning, the box is vibrating like one of those foot massage machines you see at the State Fair!

I've pulled the square box and checked it all over. It appears to have a plastic tube inside the box to blend the intake air flow through the 90* bend leading to the throttle body. The end of the plastic tube toward the MAF seems to be firmly attached to the box while the end of the tube, toward the throttle body, seems to be able to float in the box. The PCV vent line attaches to the square box but is not visible when looking through the plastic tube.

I think at certain times (temperatures?) the plastic expands and contracts, air gets between the box and the plastic tube and causes the tubeing to vibrate against the inside of the box.

I actually got the moaning sound a few weeks ago when the temperature was in the 50s and drove through a sudden shower and when I pulled up to a traffic light, turned the radio down, and it was moaning like crazy!

(I understand that the Ford Contour guys get a similar sound from their V6s, and they refer to it as "Moose-ing". It does kind a sound like a bull moose that never stops to inhale.)

 

Take a hard look at the idler pulley, if it's whining or making any noise at all I'd suggest you change it, they are not too expensive.
I had a slightly noisy, on again/off again whine on the one on my Expy - but I procrastinated and when I finally changed it the damage was done. The idler pulley going bad put a strain on my AC compressor pulley and ruined it as well.
That was an expensive lesson for me.
It may not be your problem but thought I'd bring it up.

 

Thanks for the response guys.

I’m going to take a drive this weekend and see if I can awaken the MOOSE! If I can open the hood quickly enough I’ll see if it’s the intake box PDQ Ford mentioned. Otherwise I guess I’ll take off the serpentine belt and try feel if there is play in the bearing on the idler arm.

I’ll report back on what I find in case anybody else develops a similar problem.

Does this mean my truck now has 230hp and one occasional moose power? Ha ha. What a lame attempt at some Friday humor……..

 

Most people don't realize that you can disassemble these bearings, clean, re-grease, and then reassemble them. It takes about 15 minutes, but saves the $20 for a new one, plus a trip to the store. Just be sure to use wheel bearing grease that's rated for brake rotors...it has a higher heat tolerance.