Noise after Upper Intake Replacement

I just recently replaced the upper intake manifold on my dad's friends 99 Grand Prix 3.8. It was leaking coolant pretty bad but the new manifold seems to have solved that problem. Now the car is making a terrible whining noise once warmed up. After searching the web and checking out the car I replaced the tensioner pulley and water pump because it had a little bit of play in it. I let the car warm up after this and the whining came back. It sounds like its coming from the middle or right of the engine somewhere around there. Now for the thing I don't understand, with the car running and making this whining noise if I loosen the oil cap and lift up on it a little bit the noise will stop. This is the first car I have worked on that sucks air through the oil cap. I'm not sure if this is a normal 3.8 thing or if there is a problem. Any help is appreciated.


jeff

Possible vacuum leak??

Cheak all the vacuum lines and also check the PVC valve

I agree check the PCV valve. Remember engines since ever need to have ventilation on the crank. That is why they use PCV's. It could be a stuck close PCV valve.
Also did you make sure that when installing the intake manifold all the vacum hoses were reinstalled? And no holes were covered by the new gasket that you used for the manifold?