l changed the mufflers on my 2006 Mercedes SLK with 11'' Magnaflo Turbo units. After the install the car sounded great at an idle and slow and fast speeds. At 2200 RPM to 2400 RPM under a slight load they began to set up a harmonic vibration that was deafening inside the car. All mounting brackets and welds were inspected, and the muffler is had at least an inch clearance from any body surface. Nothing seemed to help.
l had the shop put the stock units back on and the noise went away.

It is not at all unusuall for this to happem, the resonance from the different exhaust notes is picked up by the sheet metal in the body..it can be very irritating

If l remember(have not owned a car since 1994)..IDLE is set at 850-RPMs..and can go as high as 1100-RPMs./.ther Alternator will CUT IN at 2200-RPMS..even 1800-RPMS..this will cause the Car to re-act & maybe the exhaust system has a Electronic Exhaust gas-Valve for emissions..or possible the car was NOT connected for the SWAP(exhast system)..so ur AIR PUMP for the Catalytic Converter was mal-functioning-this might have been the vibration..because the PUMP-is quite ''tight'' in its build..maybe the BELTS were the trouble(meaning the AIR PUMP)for the Emissions System.

Definitely a harmonics issue, Should have tried sliding the muffler(s) back and forth ( measure the length of pipe between the cat and the muffler ) as little as 1/8'' variation could theoretically lead to this happening.

That muffler is naturally louder but it should never be ''deafening'' in the car.

Not unusual at all. Remember an exhaust needs to be tuned, no matter that the commercials on Speed Channel and the parts guys tell you. Go with a Lorinser exhaust and you will have all the tone you want, added power and wicked tailpipes.

In the Harmonics. Put a stainless system in.Started out fine, but rumbled as time we not on. Does not bother me half the time, cd is pumpin most the time. Price you have to pay for performance.At least it is not irratating as the FART pipes on Asain cars that go nowhere.