I had this noise today, after removing and refitting the inner tray of the AMS. The noise was caused by one of the 2 wires that connect to the rear of the unit, rubbing on the AMS assist motor gear (white nylon gear). I moved the wires out of the way, and the problem is sorted. When the AMS is fully assembled, this gear is very close to where the PTFE tube exits the rear of the machine (just so you know where to look).
Hope this helps,
Mick.