One of the most common complaints about flow through exhaust systems is that they cause a great deal of vibration in the car.
This is partially true.
If anyone with a 1974 has installed such an exhaust, you may notice a very resonant buzzing sound around 2500 rpm. I tracked this down to the sending devices under the seats that sense your presence in the seat.
Of course you have already disconnected these, so take the seats out and remove the whole sensing assembly. It is the plastic riveted to metal part that is causing this noise.
Since that was removed, I have had no more noise problems related to the exhaust.
Author: Doug Baxter