brofls

Only happens when driving over ~50mph. Pressing on the accelerating more than maybe 10% leads to a low sort of thumping sound from the rear behind/below the driver's seat. The harder you press on the accelerator the louder it is but it doesn't last if you keep your foot on the accelerator, only lasts about a second. Everything sounds completely normal at lower speeds though and if your foot is on the accelerator just enough to maintain the current speed this doesn't happen. Braking/decelerating sounds fine.

WRC-LVR

Check drive shaft couplings and center support for damage or worn out. Also check the transmission mount and engine mounts. Replace as necessary.