Originally Posted by mdt
I had a drone in my 6 cylinder VW after I put an aftermarket exhaust on it. In my opinion, it's less a sound than a vibration which is perhaps why film clips won't do the issue justice.
I resolved it by fitting a butterfly valve half way through the mid-section, operable by a switch on the dash. This was good for pottering around town and I could leave it open when at the race track or giving the car a boot full.
Assuming that few owners will want to take such drastic action on a new car, the options might prove to be:
- suck it up; or
- fit a more restrictive muffler, but at the expense of top-end power.
I doubt the problem can be fixed with a muffler that makes more noise elsewhere in the rev range or doesn't sacrifice power.
One of the BMW engineers was speaking to me about this very solution. That is fitting a butterfly clip in the system somewhere to keep it quiet at highway speed.