Please put your year and model in your signature. It'* alot more helpful when we can see that in order to help you.
I've pulled apart L27 Upper intake manifolds (the plastic manifold) before, and there'* nothing that can make that noise. Follow John'* guidance on checking your intake, and make sure the full intake assembly is intact and has no holes, all the way from the airbox cover (lid) to the throttle body.
Also check your vacuum hoses for leaks.
If you find nothing, try it with a helper and the hood open. If you find nothing on the intake side, look at the belt path again.