my v12 is sucking so LOUDLY ITS DEAFENING when the air cleaner cover is removed i can plug the balance pipe hole in the backing plate and the noise goes and it runs happier, whats gone wrong now?

 

Rex, just a few basic ideas:
Check the RHS air filter is not against the throttle body and somehow blocking it. Check both TBs for free movement and adjustment.
Assuming this has just started, something is different the other side, or in the crosspipe itself, as that side is doing the sucking from the noisy side.

 

when you say "happier",,, does that mean the idle comes down and it idles well?

 

Fixed an air leak on the end of manifold it seems better.

 

Hmm. On my car that opening goes directly into the AAV... When my AAV was stuck open, it was loud and revs were high.