2001 Chev Impala P0341, P0442, P0452 But Not the Problem?

Hi, I've got an '01 Impala, 3800 with 150K miles that basically runs fine. I have these three codes: P0341, P0442, P0452 but I don't think they're related to my question. The engine makes a squealing sound (like a worn fan belt) when accelerating while driving, or when advancing the throttle when in neutral. I found that I could remove the oil filler cap and the noise will stop. However, when removing the cap there's a significant amount of vacuum in the crankcase as evidenced by a "whoosh" when it's removed. I replaced the PCV valve and noticed only very minor improvement. I cannot find any external sources (hoses, fittings etc) that are leaking or require replacement. Is there another source of crankcase ventilation besides the PCV valve? Could a head or intake gasket failure cause the engine to scavenge excessive air from the crankcase causing this squeal? I have no other driveability issues with the vehicle but this doesn't sound like something that can be ignored. It doesn't use or leak any coolant or oil, but there is a burnt smell noticable when I pull it in the garage and shut it off.
Regarding the codes: gas cap and fuel pump assy replaced 6 months ago. V-belt replaced recently. Crank position sensor code has been intermittent for over two years - probably interference from wiring. Previously I've been able to get the engine light to go out by repositioning the gas cap after my wife, but not now. I think it's probably the cap again as it was an aftermarket product. Anyway, like I said the real problem doesn't seem to have any association with the codes that I'm aware of.
Any help is appreciated! Thanks.
Tony

The vacuum is routed via some plastic tubes, they are not many though. I had a 94 Grand Prix with a vacuum leak. The problem was a plastic elbow fitting that connects the intake manifold. It has like a rubber washer that dry rot and fell off. Was leaking from there and was hard to tell. The other was a plastic tube that ran underneath the battery that went to a reservoir for the AC vacuum. The Vacuum tubing I paid like $35 at the dealer and was only 3 tubes put together.

You have to chase these tube for signs of cracking. If you find one, go to Auto Zone and get some rubber tubing, get a size that the plastic tube can slide inside the rubber one with a tight fit. That is how I fixed mine.

On the sensor, it could be a worn cable on the harness. Check the cables at the sensor plug and the main plug on the top of the engine.

I hope this helps.

Actually what I meant was that I could not find evidence of an external vacuum leak, and I discount it as a source of my problem/question. But thanks anyway...

I've owned the vehicle since new, and this problem has me stumped. The engine is simply generating too much vacuum in the crankcase. I don't have a vacuum guage to measure how many inches, but the squealing noise is evidence enough that it's too much!
Again, I ask: could a manifold gasket be leaking internally that would create this noise and not present any other negative driveability issues?

A intake gasket could cause this BUT usually if it pulls vacuum from the crankcase then it should pull oil also so it would smoke. This has the plastic upper intake right? Lets look at the PCV again. When you remove it from the cavity is the "O" ring around the base of the valve that seals it in he intake? If it it missing then it will make this noise.

Yes, it has the plastic intake manifold - Bakelite or whatever.
The o-ring is in place and the PCV valve is a fairly snug fit which makes me think it's not leaking or allowing the bypassing of any air. Any other suggestions/recommendations? Thanks

I had a similar problem with a 94 Grand Prix with a 3.1 V6. I found several problems.

One was the plastic tubing, a missing flat rubber washer was missing. Made a hissing sound and one day none, but the idle was high. I went to the dealer and bough the whole vacuum set for $35.00 The whole set was only 3 plastic tubes. Another source that I had was a plastic tube that was routed underneath the battery that led to an vacuum reservoir for the AC it was cracked. I bought some rubber tubing in Auto Zone that fits pretty tight and spliced it.

The Evaporator system is composed of hoses and tubes. One could be broke, so you have to chase them to see if some is broke, loose or just disconnected. Another is canister itself, could be cracked.

Look around the Power Brake Booster. See if you can pull and plug the vacuum hose, reset the computer and let it idle. See if the code does not return.

I would not worry about code 0341, I am pretty sure that will go away as soon you find the vacuum problem.

One thing that I noticed on these engine harnesses is the cables has the tendency to break inside the insulation around the main plug on top of the engine and by the sensor plugs itself. A scanner reader that can play actual info while the engine is running, the ones that shows RPM, MAP, IAT and many other parameters, is a a great tool. You can wiggle the cables around and see if the parameter changes, if so, you have a bad cable. An intermittent problem like that will drive anybody crazy!