We have an intermittent clicking noise on our tandem that makes only occurs when pedaling and is sync with pedal stroke. Crank arms are new and torqued properly, pedal bearings are good, chainring bolts tight, seat post greased, motor (BBSHD) only has a little over 100 miles on it. It doesn’t happen on the work stand and, as noted above, is intermittent. Flat, climbing, pushing hard: it can happen anytime. Comes and goes randomly. Could it be motor related? Motor doesn’t move. It’s firmly clamped in place.