Same problem here on my 2000. I was relentless with Chevy and they ended up repairing it under the 100k power-train warranty. It was the AC tensioner and in the process they replaced the main belt tensioner which also made a lot of noise from day 1.

I too changed out the belt and the problem would go away but not for long.. A couple months later with a cold engine it would just start wailing again. It got so bad it wouldn't go away hot or cold.

It happens to all of us at some point. Last year I did the main drive belt tensioner because it was chirping. At the end of the season I noticed my balancer wobbling so put the car away and planned on dealing with it when it came out of storage. As soon as I start it up a few weeks ago the chirp is back and getting louder. Last week I had a powerbond UD pulley installed hoping that the wobbling was causing the chirp.

Not

Saturday I pull the belts one at a time and isolated the chirping to the AC belt. Tensioner was shot, what a botch to replace, I could of used two more hands but finally got the new one in with a lot of bad words and with the two hands god gave me.

All fixed!!!

sounds about right

Gates belt ,I also retorqued the tensioner and idler bolts started her up and all I can hear are my borla quads

Mine chirps/squeals loudly after any rain below 1000rpm - a squirt of silicone on the main belt stops it immediately - but it returns the next time its damp.(yes, I know a Corvette should not be in the rain but its my DD).

The low cost GM damper can rust overnight causing noise at startup then the belt wears the rust off and the noise goes away. A change to a well designed damper such as an aluminum ATI can stop this type of noise.

My 99 chirped too. I changed the belts to different brands, changed pullies and tensioners and it did not work. A couple of trips out driving hard made it chirp again. I finally changed the harmonic balancer out to a Summit SFI approved balancer and I have no more chirping. I even put the old belts and tensioners back on to see what would happen and the chirp is gone. If your balancer is wobbling it causes harmonics or vibration trying to line the grooves of a belt with the grooves in the pulley. Hope you find the problem.

I am going through this same thing on my 99 frc. It only does it at warm up and for awhile on the road and then goes away. It is driving me insane. I love pulling up to a red light and people looking over and your car is chirping like a bird. I too put dayco belts on my car recently. As far as it possibly being the harmonic balancer how chould it only chip at warm up and then go away. Wouldnt it chirp all the time if its wobbly? GM should have a recall on this

I have changed every idler and tensioner on my 99 a4 convertible. It does not chirp until you give a slight acceleration at any speed. Idles quiet, quiet under normal and heavy load, and quiet at any throttle position when sitting still. Very irritating because I can't diagnose where its coming from while I'm moving. I am going to try another gatorback belt set because I sprayed belt black on the others and now they are soft. If that fails I guess I'll try Dayco belts. I don't have any pulley wobble that can be seen.

now that makes a lot of sense - thanks Fast One!