Well...I think it's the A21. I broke out a long extension cord and went to work. A few interim tests with no change in results led me to the final test. With everything unplugged from the "media breaker" (receiver/sub/power strip w/ remaining AV gear) except the A21 and the A21 disconnected from the receiver (so the only thing plugged in were the two speakers to the A21 and the A21 to the wall, that includes the trigger switch, I put the amplifier in manual on/off mode) the A21 still made noises through the channels. Then, I disconnected the RCA cables (which were connected to nothing on the other end) and the noise went away (mostly) in ONE channel, and stuck around in the other (odd...?). The "quiet" channel still had the noise, but seriously reduced, to the point that if the other channel were that quiet I probably wouldn't be bothered by it. At that time, I tried moving the A21 to a few different plugs in the house with the long extension cord -- no change. So, unless the noise is coming from every outlet in my house, it really seems like the A21 is having issues. Also, for grins, I turned the gain down on the amplifier, and that modified the level of the noise. I don't think I can isolate any more than that unless I plug the A21 in to my neighbors' outlets, lol.
That said, a few other scary things. Firstly, I hope I didn't start the whole trouble by using a, unbeknownst to me, bad RCA wire. I have been using Audioquest Sidewinder cables that they gave me with the amplifier forever ago when I bought it. Since I found it odd that disconnecting the RCA seemed to eliminate the noise from one channel, I started tinkering. When I plugged one end of the one cable into the amplifier it went all sorts of nuts again (remember my previous post, when I disconnected the one end from the receiver the A21 went nuts), well...that issue persisted. It followed just that end of the cable through both channels of the A21. ARGH! The other cable (and the other end of that same cable) didn't exhibit that really loud humming/buzzing craziness. So...I don't know if one end of the RCA was going bad or shorting or badly soldered or some crap that was leading to an increase in resistance that started breaking down the amplifier and, eventually, my poor old Denon receiver to the point where now my A21 crackles and my poor old receiver started to as well and started to leak noise back through the subwoofer after power down, or what! But if that one stupid bloody $70 set of cables cost me this amplifier, I will be LIVID! I am not a cable snob, so to have been given expensive cables and have them be the cause is just maddening! I don't know for sure they are, but it's certainly not right that one end of one cable would cause the A21 so much trouble.
To that end, I believe I'm going to have to get in touch with Parasound (again) and re-open my old ticket and hope they'll work with me on the warranty. It was under warranty, just expiring, last year...I bloody should have sent it in then, but I didn't want to send them an amplifier that was fine and take up their time/resources. Since at that time the noise followed my receiver when I hooked up the outside speakers, I just blamed it on my receiver. I didn't have the cash to buy another...and now...well...argh! I probably should have trouble shot better back then (though to be honest, I must be going crazy, because I was almost positive last year this time when I disconnected the Parasound 100% from the receiver all the noises went away, which was also why I attributed it to the receiver) but...maybe if that cable was the ultimate cause, it finally broke down everything in the chain.... Who knows...I'm pissed, that's all I know
Make a long story short: A21 -> speakers, nothing else plugged into the A21 (not even the trigger wire), moved to several outlets in the house, all exhibited a crackling noise on the left channel, a little bit of tick on the right. If it's in my house wiring, it is certainly systemic throughout the house and mostly, from what I can tell, only bothering the A21.
Anything else I should do? Still think it's not the amplifier?
P.S. As a side note, when I disconnected my receiver from the power source completely, again, the sub-woofer started to hum. So, I went toying with that set up too. Findings:
With only the XLR->RCA adapter plugged into the sub-woofer, the minute I turned the sub-woofer on it hummed like crazy. I was holding the other end of the XLR, and as I rubbed my hand over the fins of the amplifier, the humming would change in intensity...WTF?! I put the XLR adapter down on the subwoofer, the humming got lower, picked it up, it got louder, touched the fins on the amplifier, it got lower. Is this normal? Obviously the only thing I'm changing is the grounding...it's as if the XLR->RCA adapter is acting like an antenna, though.... The minute I disconnect the adapter, the sub shuts up. If I connect the adapter to the receiver and then plug the receiver in, it shuts up.... Again, moved the sub-woofer to other outlets in the house, same response.... If this isn't normal either, I start to worry my whole house has some sort of grounding issue and I may need to get an electrician out here and then a lawyer to go after the original electricians....
edit: also, I just got done hooking everything back up and taking the A21 out of the picture. While doing so, I was verifying all my connections, cycling through sources. The sub, which uses signal sensing mode to power on, therefore was on. But, I noticed I swapped two of my HDMI cables, so I shut down the receiver and went back there to move the cables around. Keep in mind, the sub was still powered on and, since it didn't time-out from signal sensing mode, was still amplifying. So, as I reconnected the HDMI cables, when I touched the metal connector to the jack on the Denon (even though it was powered off) the sub popped. Again, WTF?! The Denon doesn't use three-prong, the sub does (so does the A21) could this be part of it? Since I bumped the chassis, that "signal" made it through to the sub due to the XLR->RCA and made it pop? I suppose normally I'd never notice it because the sub wouldn't consider that quick pop a signal and therefore, would normally be turned off, no amplifying, and I wouldn't have heard it.... Again, normal, or no? Maybe I'm just being paranoid at this point, lol....