Evening,
I wonder if there are any M3W gurus that could advise on the following please.

I purchase my 10K mile 2012 M3W in September and I only got to drive it a handful of times before Winter set in (I will only drive it in fair weather). Therefore I haven't had that many hours to get that familiar with it (so I am not 100% sure if it has always been like this or something has changed recently).

Since thw Winter came in I have been regularly running it in the garage to keep the engine well lubricated, and therefore ironically I am getting more familiar with the car over the many times I have spent watching the car idling.

Anyway standing behind the car I have noticed that the left exhaust put,put,puts away rhythmically but the right exhaust has a more stranger labored sound. When i first heard it i initially though it was some kind of exhaust rattle, but bracing the exhaust with my foot didn't alter the sound.

Here is a short video of the sound, showing the difference.

https://photos.app.goo.gl/EcCWURySb3S3S6oP9

Any advice would be most welcome. Have I got a problem?

Two other quick facts of info...

1) The M3W has a G56 ECU, but returning to stock ECU makes no difference to the sound.
2) The sound happens throughout the rev range, not just idle.