Slight vibration from exhaust
 

I recently posted about my cat problem on my hatch. With 96-98 hatches, the cat converter is mounted directly on the header. So when I took off the stock header and put on an aftermarket one, I lost my cat.

Recently, I bought a used LS teg cat and a used SIR cat back exhaust. Both bolted onto my hatch perfectly. The only modification I had to do was to dremel off the tip of the exhaust pipe by about 3" and also to bend the hangers on the muffler back. Also it took me a whole day to do this swap full of blood, sweat, and tears (I'm a newbie).

The new exhaust on the car is like night and day. I can actually feel the extra power and shifting feels more forceful. Also, the rumble is awesome!

Anyways, the problem I am having now is a slight vibration in the car at crusing speeds. When I am light on the gas pedal, a vibration in the car much like a rumble in your stomach starts to occur. I haven't had a chance to double check all the mounts and bolts for tightness, but would that be the problem at all? Or simply does this occur with some exhausts?