I have an older Trek 930 with a 250 watt Bionx system which is only a year old. I unpacked the bike after winter storage in the basement and I've been riding to/from work for the past 2 months. Starting this spring, I am getting a grinding feeling most of the time when the motor kicks in. Because it seems to come and go, I tried to figure out what the pattern is. It turns out, if the front wheel of the bike is turned even slightly to the left, the grinding happens. If I am steering right, it goes away. If I zig zag, it comes and goes as I go left and right.
I'm pretty sure the problem has something to do with the Bionx system since it feels like it is coming from the back and disappears if I turn the system off.