The ONLY way to track down the issue is the disconnect everything.
All the other channels. all the sources. leave only the TV and main speakers.
Does it still pop? Yes disconnect TV and check if no... then:
Try adding the center and rear channels, no sources: does it pop?
If still no popping. then add the Digital source. check popping.
Finally take off the digital source and add the TT. Pops?
You DO actually have to experiment if yo want to solve the issue.
Throwing stuff at it is not gonna 'solve' anything.
(new speakers? idiots... IMO.)
All the other channels. all the sources. leave only the TV and main speakers.
Does it still pop? Yes disconnect TV and check if no... then:
Try adding the center and rear channels, no sources: does it pop?
If still no popping. then add the Digital source. check popping.
Finally take off the digital source and add the TT. Pops?
You DO actually have to experiment if yo want to solve the issue.
Throwing stuff at it is not gonna 'solve' anything.
(new speakers? idiots... IMO.)