Constant chirp sound coming from something on serpentine belt

A few weeks ago I was idling my Jeep and noticed a faint chirping noise coming from the front end. It does not sound like a squeal at all, or anything like a belt that is too loose. At first I thought it was the A/C clutch but it is nearly impossible to track exactly where the sound is coming from. There are a few strange symptoms. The chirp sound is more rapid (maybe 3 chirps per second) when the A/C is on and also has a higher pitch, but the sound is still evident when the A/C is completely off, but at a lower pitch and maybe 2 times per second.

The sound all but disappears when the RPMs are anything above 1200 or so, and there is absolutely no consistency as to when the chirps start. When I start the jeep, sometimes it is very loud from the get-go, sometimes it doesn't start until after I've driven for a few miles, sometimes it is just as loud with and without A/C, and sometimes it goes away after running for over an hour. Absolutely no consistency whatsoever. I also noticed today that the chirps speed up and are higher pitched when I turn the steering wheel while idling and sitting still, leading me to believe that anything that puts a load on the belt changes the sound slightly.

I had a guy at a little oil change place give me his opinion and he thought it was a bearing in the A/C clutch but I wasn't so sure. My A/C blows incredibly cold, and there is never any burning smells or smoke from a rubbing part. Could it be the power steering pump, seeing how that changed the sound the most without changing the idle speed? I was hoping it was something simple like the idler pulley or something that had a bad bearing, or maybe even just a weird sound from a belt that is too loose. Any suggestions? I appreciate the help.

My jeep is a 94 XJ 4.0L.

Well the sound changing when the A/C is on is because the A/C brings the idle up which would cause the sound to be faster. I know you said it doesnt sound like the belt is loose, but maybe just try tightning it anyway? :dunno:

It's quite possibly an idler pulley. Easiest way is to get a long wood rod or stethoscope on each piece and have a listen (careful around the fan). You can also pull the serpentine belt off and give everything a spin and see how they feel/sound and if they have any play.

The bearing in the idler pulley can be pressed out with a bolt and big sockets or simply tapped out with a hammer. I replaced the idler bearing in my 93 ZJ a few years ago as it was squealing and generally loud.

The bearing is a standard 6203-2RS bearing, which can be had pretty cheap on eBay or directly from vxb.com who seems to list most of the bearings on eBay. I recently ordered some bearings from VXB. I was very pleased with them as they sent lots of status emails and the bearings showed up in 3 days.

Cooincidentally, I just replaced one of the idler pulley bearings in my 06 Nissan today. This was to fix a cold start squeal that the f'ing dealer swore was the NAPA brand oil filter. It was also a 6203 bearing.

Thanks for the input. I'll try both suggestions and let you know if it fixes the problem. I hope it's something as simple as a bearing or a loose belt.

I have had experience with this too. Once it was the idler pulley and another time the water pump bearing..... Good LucK !! Bill-93XJ

You might want to take a good look at the harmonic balancer, as the XJ that I just bought had a bad balancer, and it sqeaked like the noise that you are describing. Take a look at the timing cover and see if the belt looks like it is touching the cover at about the 9 o'clock position, where there is a small nub sticking out from the cover. This is where the belt was rubbing, and after looking at a few of the other XJ/MJs' that I have, I noticed that the outer ring of the balancer was up against the timing cover. The balancer had gone bad, and the outer ring "walked" back into the timing cover and was slowly eating the cover, along with dragging the belt against the cover, making the sqeaking noise. You can get a new balancer at Vauto Zone for about $55. I thought that I still had the box to get the part number off of, but I can't find it.Either way, it is a stock item for them.

My 93 did exactly the same thing. I sucked some of the power steering fluid out and filled it with Lucas Power Steering Stop Leak. I immediately noticed a difference. After about a 100 miles, the noise was completely gone.

Thanks for the suggestions. It looks like I'm going to have to wait until the weekend to actually get some time to sit down and take a look at everything. Although when I did scan it over before I didn't notice the belt rubbing up against the timing cover (not that I was specifically looking for that, I'll check again more closely). I do know a mechanic nearby who has a "stethoscope" for listening to areas on the belt so I'll have him take a look.

imethehink, I've used Lucas products in 4 of my friends vehicles all with unbelievable results. Not that I want to advertise for them here, but they actually do work. I was considering using the power steering additive myself since I thought the pump was possibly making the noise, and now that you suggested it for the same noise, that would be about the easiest and cheapest thing to try first. I just hope it isn't a bearing in the water pump, I'm tired of changing those!

Again everyone, I appreciate the help.

Well, I got some results. I drained out some power steering fluid and replaced it with the Lucas Power steering stuff but that didn't change anything. Apparently though it wasn't the power steering pump after all. Taking GREAT care not to get any on the belt, I managed to squeeze a little bit of that simple 3in1 oil onto the idler pulley bolt next to the A/C and lo and behold, the sound completely vanished. I wanted to make sure I hadn't gotten some in the wrong place and was covering up the real problem, so I took it for a 30 mile drive both in the city and highway, and when I came back and parked, the sound was still gone, with and without a/c. Now I will replace the bearing just so it never is a problem again, but at least I know now it isn't the a/c, water pump, or power steering unit. And it was a good excuse to change the power steering fluid, now I'm covered for a long time!

Thanks everyone for your ideas. Hope this helps others down the road too.

Glad we could help, and good to know it was something simple.