Originally Posted by XwChriswX

Man that is weird... But it sounds like it's coming from the front of the bay, and not the back, which would remove vacuum lines... Maybe check in see if something is rubbing on a belt or something?

Another idea would be (and you're gonna hate this) but completely go back to stock now, and then see if the noise is still there... If it is, you have a problem somewhere with your engine, if it isn't you know it is the intakes...

Then if it isn't there, reinstall everything and see if it comes back. Yes, this is completely labor intensive, but it's the other troubleshooting process I can think of...