Flowmaster Super 10's ( single chamber ) - Question

[Warputer]

I pulled off the no name mufflers that came with the car....only had her about a month now...and put on a set on Super 10's. Sounds great at idle but on the fly, sounds pretty awful. I'm thinking the original turndown set up, in front of the rear axle is part of the problem. Way too much interior "vibration" at certain rpm's. Any ideas from you guys? Anyone else running these?