No problem - I wasn't sure how much of the wiring you already had apart and were thus familiar with. I am not familiar in detail with any Winnebago's wiring except mine :-[. My last coach was a 94 Allegro with much older equipment. In any case, if the issue bothers you enough, I'd simply recommend that you go trial-and-error with this. If you know that the noise started when a certain wire was added, then I'd start there. This ground-loop stuff can happen even when volumes are set low, so if possible, remove one end of a L/R audio or L/R/Video wire while the system is on and the noise is occurring. If the noise stops, then this is a possible place to insert the ground loop isolator. If your isolator has separate ground connection wires (in addition to the RCA inputs and outputs) like mine does, you don't need to worry about connecting them for the purpose of testing, and you may not need to connect them at all in the end - especially if you don't have a ground nearby - leaving them open could cause a small reduction of stereo separation, but connecting them to ground could actually make your noise worse again. Also, if you find that the noise is reduced by inserting at one end of a cable, it's possible that it would be further improved by instead inserting at the other end of the same cable. I hope this doesn't sound too complex - here's the basic trial-and-error flow:
1) Pick an RCA L/R wire pair
2) Unplug the wire pair
3) Does the noise go away? Yes: Go to step 5, No: Go to step 4
4) Plug the wire back in, choose another wire, and go to step 2
5) Insert the ground loop isolator with it's OUTPUT side toward the equipment INPUT. You won't harm anything by accidentally getting this backward - the performance is just decreased. Leave any extra ground wires unconnected for now.
6) Is the noise still gone? Yes: Go to step 8, No: Go to step 7
7) Remove the isolator, choose another wire, and go to step 2
8) Test the system out with whatever you like to listen to. Is the sound acceptable? Yes: Go to step 10, No: Go to step 9
9) Try connecting the ground wires to the nearest available ground, and also test with the isolator connected at the OTHER end of the same wire. Go to step 11
10) Connect the ground wires to the nearest available ground and leave connected if the noise is still gone. Otherwise leave them taped off.
11) Done - but if the process DECREASED but didn't ELIMINATE the noise, you could need more than one isolator - repeat the process as necessary - I think you get the idea.
Notes:
- The video (yellow) RCA wires should not be involved in this. The ground loop adapter is only for audio, and I don't think you mentioned video noise. But to be thorough, leave any video wire (that's part of a Red/White/Yellow trio) disconnected while testing a wire.
- Once one end of the wire is disconnected, this should reduce or eliminate the noise as much as that wire possibly can. Inserting the isolator will not further reduce the noise - it will ever-so-slightly increase the noise, but hopefully leave it at an acceptable level. Point is that if you get a reduction (but not elimination) of the noise by disconnecting, you can disconnect two or more wires to find a possible combination of wires that need to be isolated, meaning more than one isolator might ultimately be needed.
- Don't forget that when the Atwood water heater reaches temperature, the electrical noise generated by it will stop!
Hope this clarifies a bit!