'91 300e, torque converter
 

Well I first thought the engine had develpoed a knock, but further inspection and a second opinion leads to the torque converter. Makes the knocking noise when the engine is loaded in gear, but cannot be heard when the car is above 5 mph.

Current solution is to go faster then 5 mph, but I suppose a new torque converter is coming soon.

Is there anything else that I should replace while I have the transmission out? I just replaced the modulator and the plastic rod thingy...

Based on what I recently found, might be a good idea to just replace the reverse clutch plates. Seems they wear out first.
When you shift from park to reverse is there a delay before gear engagement, as compared to when shifting to drive. This is first indicator of wearing reverse plates. Pretty easy job when the tranny is on the bench.
And of course, do the front seal on principal.

DG