I've put the filter back in. Touching the body and the barrels did not make a difference, nor did unplugging the interconnect to the sub plate amps.
For clarity, the speaker system is the open baffle Wedgies on top driven by a NAD C372 power amp, and 3x8" servos in an H-Frame on the bottom driven by Rythmik HX300 plate amps. All of the components in the chain are plugged into a Panamax power conditioner which is plugged into a single wall outlet.
Also, the sound I am talking about is not a low frequency hum coming from the woofers but rather a higher frequency hiss/crackle coming from the tweeters. The best way I can think of to describe it is that it sounds like static, like the sound you hear from a radio that is not tuned into a station, only muted. It is in both speakers. It is louder on the back side of the tweeter than the front. It is not loud enough to hear over music playing at a normal volume unless I put my ear right up to the tweeter. However, when the music is playing very softly or everything is on but no music is playing the sound can be heard from the listening position.