Pats Scanner Bro MFC 4420c

was cleaning the heads and when removing cover opened the glass where scanner motor etc was..when put back together their is a clicking noise as the motor tries to bring the scanning head back to ready position. It is as if the head needs to travel farther back, but since it is pinned to the left side of the unit the motor keeps trying to pull it (for 3 seconds or so). The top portion of the 'loop' in the band appears slack when this happens. Have tried readjusting the starting position of the head etc. Any thoughts from those of you that have opened these up??