1998 Trans Am. LS1, stock pulley system. Chirping at idle. Worse with some throttle. Chatters more/more loudly.

Removed A/C belt. Same symptoms.

With the stethoscope I can hear it on the idler pulley AND on the body of the alternator.

The noise is worse with a new belt than with the old belt.
Has a new idler pulley, new tensioner (with a new pulley).

Belt dressing made it so much worse that I spent time with a brush and carb cleaner to remove it from the belt and pulleys.

Removed the accessory belt. No chatter/squeal.

I’m open to any suggestions. I’m out of ideas. Thanks, gentlemen.

Could be the bearing in the alternator. Did you try spinning the alternator by hand when the belt was off? Spin all the pulleys for that matter when the belt was off. Usually you can tell where it’s coming from this way. Also, sometimes a quick shot if wd-40 into the suspected pulley will help diagnose. If the noise changes at all, you have found the problem. Wd-40 needs to hit the bearing though.
Word of caution, spraying wd-40 into the alternator is not the best idea...

Thank you, sir. I thought about that. However , I did not know how to test it and I had not asked either. I will give that a try and see what happens.

Tayj6, the alternator didn’t reproduce the squeak when turned by hand. A brief shot of WD didn’t change it when sprayed from the rear of the pulley toward the front.
So, without a lot of confidence I purchased an AC Delco tensioner pulley and a Continental (formerly Gatorback?) belt.
No squeak.
Ran it for an hour this afternoon enjoying the drive without all that disturbing racket.
Thank you for your time and suggestion, sir.

Awesome! Glad you figured it out and it wasn’t too expensive.