[Lord of Hog]

This is rapidly becoming the bane of my life entailing many hours underneath my X-plate 2.5 cursing the exhaust, the car and life in general.

The factory fitted rear box disintegrated at around 90k and I've spent the last 12000 miles fitting and removing a succession of replacement boxes all of which produced a loud resonating boom between 1200 and 2400 revs, louder than the engine in many cases which is a shame when the engine sounds so nice.

I've tried fitting additional soundproofing to the boot and that has improved things a little but I'd love to have some suggestions as to how to fix it.

Is it resonance in the boot/rear bumper area?
Is it the result of the pipes being too short and the bumper magnifying the sound?
Are the hangers too short (and if so how to fit longer ones while avoiding the pipe-knocking-on-the-crossmember sound)?

To be quite honest I'm running out of ideas so any suggestions would be gratefully accepted.