My PSW505 is making a chirping sound under certain conditions. It seems to happen at certain frequencies or tone durations. If I hook up my PC and do the Windows 7 speaker setup test and test the subwoofer channel, the chirping happens every time. I am using the LFE input on the sub and the volume is at 50%. Does anyone know what part may be damaged or how I can fix it myself? I don't want to pay for return shipping for the whole unit to get it repaired. Thanks.