So, my '06 M coupe has recently started doing some irritating shuttering. When coasting in 2nd gear, just shy of 4k rpms (3700-3900) it bucks back and forth. It feels a lot like a bad shift (but I'm not shifting) and it also happens if there is only a small amount of throttle applied to maintain the revs. If coasting, the bucking stops as soon as the revs drop below 3700ish. Under acceleration it behaves normally.

Interestingly, I've tested 1st-4th gear and only 2nd bucks. I've also tested going up/down hills & flats. When going downhill it is the most exaggerated. It's noticeable, but not quite as bad on flats. Uphill doesn't feel as bad for some reason.

I'm going to take it to the dealer in a couple days, but I was hoping you all might be able to provide a little insight first. Any input would be appreciated, so I don't go in there looking like a total fool.

Thanks in advance.

So since it's in only 4th and a specific rev range, can you say it's actually at a specific speed? Have you tried different gears at that same speed (range)?

It's actually only 2nd, but iirc it's usually right under 40mph. Something around 36-38 i think.