Try and figgure out where it's coming from. I would say likely some restriction in the intake. Expirement with different parts, I've seen GM use something like that of a restrictor plate to help reduce intake noise... Worth a look. Have someone rev the car while you listen to see where it is actually being caused.

 

I have got a really good idea of where you are, and what it is you do.

Keep up the good work brother.