anthem,

I say again: I pulled the power plug out of the TRef, and the noise was still there. It can't possibly be coming through the power line from the P20, or from anything else through the power cord.

All,

After a couple of days of careful listening, I have heard no rumble noise from either speaker. So it looks like swapping the speakers cured the problem.

There seems little doubt the intermittent rumble was caused by wifi interference. When I swapped the speakers, I expected the noise to either stay with the same speaker (what was right was now left), or it would show up in the new right speaker (what was left was now right). Instead, neither happened. They both are now noise free, at least for the moment.

What is going on here? I see two possibilities. First, that the originally right speaker was more susceptible to wifi noise, either due to subtle differences in circuitry, or perhaps because of component drift that let more noise through. Moving it to a different location helped.

A second possiblity is that when I swapped the speakers, they didn't end up in exactly the same places. The wifi system is operating in two bands, 2.5 and 5 GHz. The wavelength for the 5 GHz band is only 6 cm. (2.4 in). So if the wifi environment forms standing waves in the listening room because of internal reflections, there might be only 3 cm distance between a node (minimum) and an antinode (maximum). It is possible that the original right speaker was positioned so that a vulnerable part of the internal circuit was on a maximum, producing the noise. Then when I moved the left speaker to that position, it may have ended up in a slightly different position, maybe on a minimum. So, noise problem solved. This is just a theory, but if true, then noise problems like this might be solved by repositioning the speaker only a short distance.

Whatever the truth is, at least the problem appears to be solved for now.

As I said elsewhere on this forum, GET should work on how to eliminate wifi noise from getting into the subwoofer amps of their speakers. Filtering? Shielding? There must be a way to do this. As more and more wireless devices are used in homes, this is going to become a bigger problem.

Charlie

Thanks for the update Charlie!

WiFi interference with the T Ref amp makes some sense, since the problem persisted after unplugging the speaker from the power source until the amp capacitors drained down.

Rick

I forgot to thank anthem for suggesting that I swap the speakers. Thank you, anthem.

Charlie:
Just think, A simple suggestion of swapping speakers has solved your problem. Besides fixing the issue, you also got a Great workout moving speakers around.

I have wifi gear (router and cable modem) in close proximity to my speakers and have never heard any "rumble noise" caused by the wifi.

My wifi runs at 2.4 only and is approximately 2 feet from one speaker and 6 feet from the other.