When I bought my Pro Connect LX (Deraileur Gears) last august but within a couple of weeks there was an intermittent rumbling like a chain slip noise when the power was on yet when the power was swithched off the bike pedal silently. I did wonder if it was the motor. 50 cycles suggested I look at the chain to see if it is rubbing against the chain guard. I did but I found the problem myself. The gear cable had stretched and the chain seemed dry. I adjusted the gear cable by tightening it and fine tuning the gear changing and lubed the chain. Now the bike rides like the reviews say it does; it is silent and it is smooth running and a delight to ride. The rumbling noise has gone but when the gears dont change as sharp as I like, I fine tune the changing by adjusting the gear cable at the deraileur end.