Squeal/Chirp

On my 98 ZX2 I have a loud squeal/chirp that I thought was a bad belt(well the belt was bad just not this problem). Changed the belt, no luck. Got to checking, it seemed like it was coming from the alternator, changed it still making the same noise. It only happens when the car is warm. Very loud when it gets hot, but it will stop when I pulled the dipstick out or remove the filler cap. It is at the worst when the car is idling, sometimes at highway speeds, but not as bad. Got under the car and it is coming from the engine on the drivers side of the catalytic converter. Took it my trusted mechanic (only one I trust to work on my cars without jerking me around) and he wasn't really sure, he thought it might be emission related, but didn't have any way to check it. But, he did tell me to take to a shop down the road for a second opinion. This guy jacked it up and looked under it. He scratched his head for a few then called someone; think it was the local Ford dealership. After about 15 min he said he thinks it is the flywheel, cracked or bolts loose Well I took it back to the first shop and told him what the second guy said, and he did not think this was it because the noise stopped when the filler cap was removed. Told him that I was afraid that I would have to take it to the $$$$$$ place down the road (the Ford dealership), and he said that’s what he was thinking.

Definitely a strange problem..........couple of thoughts on it though: It seems like that since it stops when you pull the dipstick, or filler cap, it may be reducing some kind of 'pressure' that is normally released, but isn't for some reason, and the 'chirping' is caused by it release where it shouldn't????? PCV valve, crankcase vent, hose, etc.? Then again, what do I know, just guessing....

The guys at the shop now say it is a bad oil separator. Going to get it fixed later this week.