ET was here said:
take the car to any exhaust fitment centre and get them to check the source of the noise
the timing of working on the exhaust and the start of the rattle is too close
I can vouch for this
Just recently I finally replaced the defective-broken engine mounting on the E39-530d
and almost the same day, I would get a rattling noise from under the body, and always when the car was warm, and always just at the slow speed pull away
So I put it back on the lift, whilst still running and hot, and then applied brakes whilst engaging drive and reverse, whilst the exhaust technician stood underneath, trying to source the sound
The new engine mounting, had (due to its new condition and rigidity) basically changed the positioning and alignment of the engine just suffieciently to cause the exhaust to knock on the central mounting bracket
a bit of heat and extra rubber grommets, and the problem was solved in 2 minutes
seeing as you very recently had exhaust work done, I would rather suspect that this is the issue, and your engaging releasing the clutch is causing just enough twisting motion of the engine-gearbox assembly to now cause the modified exhaust to touch against the body or a mounting bracket
it is the easiest and cheapest fix,
I wont discount the fact that possibly and purely by co-incidentaly the clutch decided to go "south", but my first call would be to investigate the exhasut possibly touching somewhere now
