I've recently connected my speakers (Elac Cinema 2) to my receiver (Yamaha RX-V630) and have this annoying problem. Whenever I change from one DSP program to another (i.e Prologic to Prologic II) I get a thud sound from the subwoofer. The subwoofer is connected via the LFE jack on the receiver. Does anyone know what could be causing this and could the sub or amp get damaged ? Also can someone explain what a RCA ground loop is?