That would be a Motordyne. Many others utilize the hemoltz resonance method to eliminate drone. I had a Ark Grip on my 370 and it used the same as well. Heck, even the cat delete pipes made for the Z platform were offered with the same design to eliminate drone and rasp. they were called "ART" pipes, short for Acoustic Resonance Tech.



So this idea has been around and proven for quite some time. It's a shame no one really makes any exhausts for the e60s. The ones that do are ridiculously overpriced for what you get. The Motordyne above is incredible craftsmanship and is right around $1800 and worth every penny as you can see. V band clamps, full polish, titanium pieces, etc. We get a muffler on a 2' pipe for $1000.

 

Put it this way, your under carriage get another set of balls.