Wheeling my K9 Wee back last night the normal click of the chain on sprocket was accompanied by an unusual knocking sound. After putting the bike on the centre stand and rotating the wheel backwards I was able to identify the knock as being near the rear sprocket. The sound, though not loud, was accompanied by a vibration of the chain. The knock didn't occur when the wheel was rotated forwards. Both front and rear sprockets and chain appear to be in good order. The wheel seems to have no play in it. I'm wondering if this might be a wheel bearing issue. Any thoughts?