I installed a decent Home Theater in my own home. I just used an existing lighting circuit that was in the area. When I turn on a light in that room (same circuit) the subwoofer makes a thumping sound. I used quad shield RG-6 and didn't run it parallel to any electrical that was near by.

Any ideas on what is causing this?

Thanks,
Byron

Byron,
Does the power plug on the subwoofer have 2 or three conductors?

Switching noise? What kind of light, and what kind of switching? If just a regular switch - try a dimmer....

Electronic Ballast? Could it possibly be causing harmonics on the neutral? Cheapest solution since you're an EC might be a dedicated circuit for the AV equiptment..
But if you're really into spending cash, there's a link around here someplace to some faceplates that are supposed to make your system sound better
https://www.electrical-contractor.net/ubb/Forum1/HTML/007372.html

That's a problem right there. RG-6 isn't designed for use at audio frequencies, and the shield (since it's being used as an unbalanced return) is acting like an antenna.

You need to get some Belden 8451 (or it's easier to strip brother, 9451) from an electronics house. (Radio Shack used to carry a wire very similar, ask for two-conductor foil shielded cable.)

Connect it as follows: ( I'm assuming use of RCA phono plugs on each end)

Red wire: To tip on each end
Black wire: To shell (or "crown") on each end
Shield (bare)wire: To shell on one end only. Important: Make sure the shield does NOT contact the shell at all on the end opposite this connection.

You may need to experiment, but connect the end with the shield tied in on the SOURCE end first.

That should eliminate most if not all of the pop. Also, a surge protector at the sub wouldn't hurt.

And if you have money to burn, you can always get Monster cable. It'll work well but is super expensive.

PM me if you have more questions/need more help.