M5 Expert (>4000)
Join Date: Mar 2011
Location: Ontario, Canada
Thanked 1,418 Times in 1,032 Posts
Could it be the engine pinging (detonating) under high load? I can just hear a very light rattle in your clip. These cars will give a quick ping when the throttle is snapped open in neutral as well. Search for "detonation" or "pinging". There have been a couple of threads recently.
By the way, it's not a good idea to floor the gas pedal at 1500 rpm in any gear but especially in 6th since the revs stay lower for longer. It puts a very high load on the rod bearings before the oil pressure is fully developed. Safer at 2000 or more.