Buzzing sound between 2-3000rpm

Alright..this is bugs the hell out of me.

I have 96 vtec and i get some sort of buzzing sound under the car when between 2-3000rpms. Not only accellerating..When I push in the clutch it goes away. I have had the car up on the hoist and there was a crack in the bracket near the cat. They fixed it and then it came back.. I was told it was the heat shield. One of the bolts rusted through and they just put a strap round it. The noise is still there and its annoying as hell. I already searched the forums and most of the problems seem to be the heat shield...just wondering if anyone knows something else that it could be?

Thanks in advance.

It could also be your flex pipe, the flexible piece on the part after the oxygen sensor on the downpipe.