Hi I bought a PMA-980R online. It is ok accept the source selector knob. It jumps between sources when i try to change by the knob, it jumps to CD;TUNER;TAPE by clicking 6-8 times before stopping whereever it wants. It is OK with the remote it comes to place at once;if i touch the knob it may click by remote too. Can this be caused by dust inside the knob? Thanks.