[WARP TEN]

Originally Posted by XfireZ51

I would try some styrofoam or foam over the top of the spare tire so that it deadens any resonance of the hatch floor. Could it be that the spare tire carrier creates a BOOOM Box under the hatch floor?

Hi Dom--
Many years ago when I was testing a Power Effects system (lots of resonance!) and researching our resonance problem in general I actually had an acoustical engineer (ironically from Outboard Marine) instrument my car and evaluate the causes and suggest a solution. He developed graphs showing precisely what RPM and frequencies the two main resonance points were and showed calculations required to make a Helmholz resonator for each of the offending frequencies, which of course is what the stock and Corsa systems use.

They also researched whether it might involve something like you mentioned called "cavity resonance". Meaning it is enhanced or diminished by the cabin itself (or maybe the tire carrier?). I had asked because it seemed less with the top off. Their conclusion was that it was not cavity resonance but solely caused by the exhaust and the natural harmonics of the engine. It seemed to be less with the top off only because it was generally noisier with it off and it was therefore not as noticeable. --Bob