I have an issue I need some input on and have done as much searching as I can to no avail.
Anytime I lay into the throttle in 2nd gear, as I get into the upper half of the rpm range I start getting a vibration from the rear end best described as being like axle hop. Problem is it does it with traction control on or off, regardless of road condition (rough or smooth). It seems to me it used to be only at the very top of 2nd, but it is now showing itself lower in the rpm range, and only during aggressive throttle input. It does not trigger the traction control light if DSC is on. The one time I didn't get out of the throttle fast enough it made a terrible racket and thumping.
I don't speed away from stops, smoke tires, etc. and don't feel I have mistreated the car in the 1500 miles I've owned it. The problem showed itself again this morning with the family in the car just merging with traffic. Its annoying because after all this time looking for a nice low mile (25k) M5 I'm afraid to actually use it beyond driving it like a Honda.
I had BMW replace both rear sway bar brackets this week (one was broken and one was cracked - have to assume from prev owner), and the tech indicated the rear trailing arm bushings were a little worn, but am not certain they would contribute to this issue (I'll be honest - I don't know what rear trailing arms do at all. I have to schedule the car in for that repair). He said the diff mounts were fine.
Doesn't appear to be an issue in other gears, but not really hammering on the throttle for fear of breaking something. What else should I look for?
The clutch pedal has a little vibration feedback on dowshifts, the tires are recent Dunlops, and there are no unnusual vibrations in the trans or shifter (those were some of the things mentioned in search results). The car is completely tight and solid otherwise.
Thanks in advance and sorry for the long post length.