[Incompatible]

Something to consider. If you look at a number of exhausts on BMWs you will see a rubber and metal object bolted to the muffler or close to it on the pipes leading into the muffler, this is a frequency attenuation device. It dampens the frequency within its designed range (drone). A friend of mine who I trust, told me his even has a frequency indicated on his.

I have played around off and on with my Ford Expedition and it's straight through Magnaflow muffler which has terrible drone. I simply attached a 1 pound lead ingot to the intake side of the muffler and noticed a difference in drone level and quality. The change wasn't a night and day difference but it did take the hollow edge off the sound and slightly lessened the volume. Placement along the exhaust is important and seems to have it's greatest effect on or up against the muffler itself.

It might be worth the minimal amount of time and effort to pick up a pair of these from the local salvage yard and attach them to your mufflers. It might help.