The noise is driving me mad! AAAAHHHHHH! Help.

OK, not really mad, but very annoyed.

'97 Jeep XJ, 4.0L, 170K miles. Squeak/squeal/chirp from something in the accessory belt drive. Here's what I've done so far:

Replaced the tensioner pulley and bearing - figured I'd do the cheap, easy thing first. Still noisy.

Replaced the mechanical fan shaft and bearing in the bracket that supports the a/c compressor. That was fun. Still noisy.

Replaced the a/c compressor clutch bearing. Easier than I thought. Still noisy.

Replaced the water pump. Still noisy.

Tried a different (old) belt. Still noisy.

Cleaned the original serpentine belt with brake cleaner, used a wire brush to clean the grooves of all the pullies. Still noisy.

Tried less belt tension. Still noisy. Tried more belt tension. Still noisy. Removed belt and started engine. NO NOISE! Not useful other than that it tells me the noise is something in the accessory drive, but I knew that.

All the old bearings I removed were smooth and quiet when turned by hand. Everything works perfectly, no shimmy, shake, or wobble in any of the pullies. Noise happens at idle, under acceleration, when slowing down, with a/c on, with a/c off, with all electrical loads on, with all of them off, doesn't go away after it warms up....it's not the screeeeeeech of a slipping belt, it's more of a squeak/chirp that increases with engine speed and sounds for all the world like a dry bearing. Only thing left is the power steering pump and the alternator, both of those turn smoothly and quietly by hand with the belt off.

I'm tired of throwing parts at it.       

I know nothing about these, but I know how frustrating tracking down persistent problems can be. One thing I didn't see mentioned - perhaps because it's irrelevant - is the crank pulley. Do these use a balancer, or a pulley with a rubber damper? If it's the latter, I've had the problem of the rubber separating and squealing as the two sections spin at different speeds.

Take some scotchbrite and a pair of long reach pliers or forceps.

Hold the scotchbrite against the running belt, back side and front. do the pulleys too. Be bloody careful, it's running!

Do this until the squeak goes away.

Take a marker and put a line on the damper ring down to the hub, then run it for a while.

Mechanical belt tensioner, or spring loaded?  The pivot bushing will wear and allow the pulley to go a bit out of line.

Eyeball the alignment of all the pulleys.  You might be able to see something a bit farther in or out.  Old Volvos mounted their alternator in rubber bushings, and they always had a chirp due to the rubber bushings compressing.

I have a 99 Durango that had the same issue. I think keep and molar had merged by then? Anyway. It was the idler pulley. Even with a brand new one it kept squealing.Pulled the bolt, slathered the bolt and bearing interior with synthetic grease and reinstalled. 5 minutes of running later it was quiet. 3 years later still quiet.

If none of the other things mentioned seem to be a problem i've fixed many mysterious belt squeaks by installing Goodyear gatorback belts. They are very good.

Molvo had what I thought was a bad idler pulley that was driving me nuts. Buddy Mustang tells me to get a handfull of silicone sealer and smear it on as much of the ribbed surface of the belt as could be reached. with the engine off.  Fired the car up and the squeek was gone and has not yet returned. ¯\_(ツ)_/¯  Claims that the silicone filled some void in the system that was causing pulley queefs.

Pete

Damn you...

My vacation starts tomorrow, I have to wait a whole week to use the term "Pulley queefs" at work. 

Can you (did you?) pull a belt at a time and run it?   Trying to narrow down the source

Maybe I missed it, but I see belt changes, but I see no mention of a new belt.

Did you check alignment of the pulleys?

Did you check the crank pulley/balancer? The rubber between the pulley part and balancer is know to fail and the pulley part can walk front to back causing belt alignment issues and will sooner or later separate totally. Had a 95 cherokee with the 4.0 do it to me.

gearheadmb said:

If none of the other things mentioned seem to be a problem i've fixed many mysterious belt squeaks by installing Goodyear gatorback belts. They are very good.

+1 this solved the same problem on my Tundra. Had to find NOS belt because the ones for that engine are no longer made.

..the correct solution is probably alignment of pulleys but I definitely didn't have the ability to fix that. 

Came here expecting a thread about cicadas.

My bet is a bad bearing in one of the accessories that only makes noise with load on it from the belt tension. Go get a mechanics stethoscope and track it down. 

I think I fixed it.

Installed a new harmonic balancer/crank pulley and a new belt, while I was under there working on the crank pulley I took a good close look at the alternator pulley (it's down low on the passenger side, hard to see from the top), and it had a lot of rubber/rust/dirt/etc crud buildup down in the grooves, so I spent some time with a pick, small screwdriver, and wire brush cleaning all that out.

The original harmonic balancer wasn't really that bad, had some cracks in the rubber ring but no chunks missing, it didn't wobble, and was still straight - but the center bolt that secured it to the crank came loose a lot easier than it should have. When I put the new balancer on, I made sure to use Loctite on the threads and torqued it to spec (80 ft-lbs).

New belt on, it's all nice and quiet and smooth - even with the A/C on, headlights on high, rear defroster on, hazards on (to put as much load on the belt as I could).

Fingers crossed