hello all
I just replaced the exhaust system on my 1978 244 with m46 tranny. Due to its age and emmission laws here I was able to have the resonator and cat removed. This leaves a long 2" (i think) pipe from the downpipe to the rear axle. It is then routed under the axle to a new stock rear muffler. The idea was a little mre power and the old cat was suspect of being cloged. I knew this would mean a little more noise. What I did not expect was a resonating vibration at certain throttle settings. I dont have a tack but I would guess it is about half throttle. It also appears in between shifts while the engine throttles down.
The system is suspended from three rubber mounts, with no metal to car contact anyplace I can find. The system also "floats" pretty well with a fair amount of travel.
My question is this.. Can the pipe itself vibrate (like a long guitar string)? I was thinking of welding a section of angle iron to side of the long section of pipe to dampen this. I may just clamp it at first to test.
Has anyone else seen this?

Joe