About a year ago, I had an exhaust system custom made for my '83 Crossfire Z/28. 2.25" pipes off the exhaust manifolds, into a Y-pipe, 3" High flow Catco, 3" pipe into a Flowmaster and stock appearing 2.5" pipes. The Flowmaster droned too much so I switched it with an OEM replacement. Droning was better, but not gone. And there is a resonace I don't like either. Frankly, I don't like the sound very much either. It does perform better than the old clogged stock system though. I guess this is why the OEM's spend so much time on NVH. Anyhoo, I've spent way too much money on the system to sh!tcan it now. So I'm looking at ways to fix it. I've heard that perhaps adding more rubberized hangers might help with the resonance. Or hanging clamps with weight at specific points to act as dampers. Any thoughts?

sounds like you want a deeper rumble. Try a 3 inch internal diameter chambered as the midpipe. if it's still a little loud after you install a 31 inch midpipe you can always add to 12 inch chamber mufflers for your dual exhaust effect.

So, this morning I was fiddling around with the Camaros.

I rechecked the timing on my Crossfire. Previously, I had advanced the timing 4*. I noticed that as I advanced it even more - the motor ran smoother. I estimate (the marker is now beyond the tab), that I advanced it an additional 4 or 5 degrees.

I only took it for a short spin but, motor runs much smoother, exhaust drone and resonance are essentially gone.