Subwoofer - Thump or Pop
If your subwoofer(s) "thump" or "pop" when you are changing inputs on your receiver don't automatically blame the subwoofer. The subwoofer will only reproduce the signal sent to it from the AVR(Audio Video Receiver). Whenever the receiver loses the audio "codec"(signal) it should mute all of the pre-out jacks for a short period of time. So when you change inputs or change listening modes and you hear the subwoofer(or any speaker) "pop" this indicates that particular pre-out jack is not being muted....or not being muted for a long enough period of time. This can indicate there is a failed diode / circuit in the receiver. You can have the receiver serviced but before going through that inconvenience try a couple things to minimize the problem.
Adjust the gain control on the subwoofer in conjunction with the bass level control in the receiver. You may find a combination of settings that maintain correct bass levels but reduce the annoying "pop" a bit.
Check the Input settings for each input device. Set the AUDIO INPUT setting to the specific audio signal instead of "Auto". For example, if you know the component will only send a digital signal...select the appropriate setting. This may be "digital" or "bit-stream" or even the type of cable/input used such as "digital co-ax input #1". Do not use the "auto" or "auto-detect" setting. The "Auto" setting can cause the receiver to take a little longer to "lock" on to the audio signal. This delay may exceed the time the pre-out jack is muted----and you end up with the "thump" sound from the subwoofer.
Power Sound Audio