M140i rear thud when engaging gear + low-speed shudder

[Crispy0001]

Hi everyone,

I have a 2019 BMW M140i (ZF8 auto) with the following mods: Stage 2+, gearbox tune, engine tune, HPFP, downpipe, Wavetrac LSD, BC Racing adjustable suspension, full Powerflex bushes, M240i rear subframe brace. Car has 93,500 km.

Recently I’ve developed a single thud from the rear when engaging D or R, plus a low-speed shudder/vibration (0–20 km/h) under light throttle, mostly in 1st and 2nd gear. It smooths out with more throttle and the car feels fine at motorway speeds.

A mechanic suggested the aftermarket bushes are the cause and recommended going back to stock and servicing the gearbox, but I’m not convinced as he didn’t identify a specific fault. Has anyone experienced something similar?

Thanks!