The parking brake would be a good theory only if you had set the parking brake when you stopped.
The throwout bearing does not know whether you are starting out in forward or reverse. However, the transmission mounts, guibo, rear axle assembly bushings, rear shock mounts, and even the engine mounts all shift the opposite direction when you start out in reverse. We have a long list of suspects here. Fortunately, the problem is not urgent so you can wait until it develops into a clunk and is easier to find.
If this were an early e46, my first suspect would have been the dreaded cracked body around the rear shock mounts.