2016 M6 Gran Coupe trunk thump noise question

[BMW940315]

Looking for sleuthing help. I have a 2016 M6 Gran Coupe, 6 speed, with only about 26K. Have noticed a “thump” sounding coming from the trunk area, …. like something is sliding, upon going from a stop, up an incline. Sometimes, same kind of sliding “thump” upon braking or upon quicker acceleration. Have emptied trunk and do not see anything loose. I totally baby this car, always garages, pampered, etc. any ideas?

[Mandrake]

Have you looked in the battery area under the trunk floor? Could be the tire pump or other supplies?
Love to see that 6-speed!

[Aliendex]

Remove the carpeting in the trunk area, take down the back seats and go for a test-drive for a more noticeable sound of the issue.

[BMW940315]

Thanks for the suggestion, and have done that, including taking everything out: trunk liner, fix flat kit, etc.

Yes, the manual six speed is sweet but had to order the car, as sticks are not exactly popular.

Will try getting another person to drive, and myself in the back, to see if I can locate it. Definitely something sliding, but not far.

[TinCanSailor]

Had the 3rd brake light over the rear window had the recall work completed. BMW issued a recall about a year ago to address an issue where the 3rd brake light would come unbolted and could liberate itself from the car.

[BMW940315]

Thank you for the suggestion. Unfortunately I think I may have found the answer. In January of this year, I took the vehicle in, because I had noticed a shimmy in the steering column upon first driving. Turned out to be a differential fluid leak. Of course, taking care of that required quite a bit of work and disassembly. Started noticing this thump a few months afterwards. Am afraid my control arm(s) have either bolt attachment issues, or have failed somehow. Taking it in tomorrow. Car only has 26.5K on it and is never treated roughly. But it is very heavy. Seems suspiciously coincidental with the differential work timing, but may only be that.

[BMW940315]

Many thanks for the responses I received. Found the answer. In doing the differential work(had a leak) the dealership technician failure to torque down on some mounting bolts, which had loosened. They have since been tightened….no charge, am assured no damage down, and note made NOT to have that person work on my car in the future.

Over years and which other cars I have owned, upon returning from the dealership for “maintenance” have found various things left I completed under the hood….like attachment bolts, leftover tools, etc. always good to check things yourself and trust your instincts.

[BMWRog]

Thanks for letting us know the final outcome. Hopefully there will be no long term damage as a result of this previous bad workmanship.