2002 Buick Century loud squealing problem

I know this will sound funny but pop the belt off and spin the ac pulley by hand and see what it sounds like?

If you were told to replace these things, how were they diagnosed? I suspect someone just guessed based on your description of the symptoms. That's hardly a diagnosis, and you're seeing the results in your wallet.

If you paid a mechanic to diagnose the noise, he should have done the work too. Very often we are really sure we know what's wrong, but the definitive test is when we replace the part we diagnosed. When it doesn't solve the problem, we have to remove that part and start over. We hate that as much as you do, but it saves you from buying unneeded parts.

All of the parts you replaced could cause a belt squeal, but it's usually fairly easy to diagnose which one is doing it. First, sight along all of the pulleys and look for one where the belt is peeking out on the side and is not in line with the rest, even by 1/16". That pulley or the one right before it is turned or tipped due to a worn bearing. That forces the belt to slide sideways across it as it goes around it, and that sets up the squeal.

You can also dribble a little water on the smooth backside of the belt. If that belt is causing the noise, it will change when water is on it. Water tends to quiet a belt squealing on a tipped pulley, and it makes it louder if it's due to a tight pulley.

So you hear squealing without the belt on the car?

So when you spin the ac pulley by hand without the belt off you hear the same noise?

Thank you for that suggestion. Was the leak the source of the noise or was the hot exhaust gas making something else make the noise?

Dandy. Logic dictates an exhaust leak is after the engine so there shouldn't be any effect on power, but what happens is between the pulses of power, the momentum of the exhaust gas flow creates little puffs of vacuum, and that can draw in outside air. The oxygen in that air gets detected by the oxygen sensor as a lean condition, then the Engine Computer tries to make the mixture more rich. No matter how much fuel it adds, that oxygen keeps making the O2 sensor readings say "lean". You're burning excessive fuel with no oxygen to go with it.