I researched this as best i could on this board and the only thing i found was a thread that it ended up being the cat. I just put on Edelbrock headers, magnaflow cat and a hooker cat-back. Car runs and sounds good...except there is this whistle that builds up as the rpms climb. It's not as bad when accelerating moderatly b/c the exhaust noise drowns it out, but when accelerating slowly, like under 2000rpms you can hear this irritating whine or whistle. I retorqued all the header bolts,y-pipe to collector bolts, and clamps on the cat, and none were loose, there seems to be no leak under the car when i crawl around under it and feel with my hands around each joint i don't feel/hear anything from any of the cat joints or the collector to y-pipe joints. It seems to be focused on the passenger side which makes me wonder if my air pump or air tube or something is leaking...any help guys???

Thanks for anything
Josh

 

Sounds like you are on the right track with the air pump & pipes. A leak small enough to make a whistling sound may not be great enough to be detected by feeling. Look for black carbon deposits coming out of the joints instead.

 

alright thanks Rick, how long does it take for deposits to build up to the point that they are noticable?I was gonna put a little teflon on the threads where the backfire valve or whatever that black thing that threads onto the air pipe on the headers is called. I'm gonna put hose clamps on some of the black hoses that have just those plastic deals on them. I don't know what else to do but this noise is getting kinda irritating with an exhaust i am otherwise in love with.

Thanks Josh

 

A loose vacuum hose somewhere will whistle as well.