First off, I want to say thank you to all of you who have helped out in this thread. It is very much appreciated. Sorry for not responding sooner as I have been juggling too many things lately.
To summarize -
My original pedal board configuration was set up to go through a Rockboard patch bay. To me it was a variable so I wanted to remove it. I disconnected the FM9 from everything, including my expression pedal and left only the XLR out 1 going to the FRFR, power cable coming from the wall and a guitar cable.
Whenever I would use a high gain amp, I would get a lot of noise. I have 3 les pauls, each with different pickups. My main LP is a Slash sig model 2020 with the Slash pickups in it - which are super hot. My other standard has Alnico II's in it, but it also has copper shielding in the cavity. My custom has no shielding but has Pearly Gates in it. All 3 guitars had noise, but they had different levels of it. The Slash model was the loudest and the custom was the softest. All of the guitars had the same type of noise though, a buzzing. Switching to a more tame amp like an AC20 Treble, that noise went away. Also, when touching the strings, the noise dissipated as you'd expect due to grounding. Adjusting the input 1 block gate threshold and ratio seemed to clear it up for the most part, along with dialing back the gain on the amp. After all, there is always going to be some noise, I just don't want it to be so egregious that it ruins a live show.
My next test was to use my actual rack that I use at shows, which also has a Furman power conditioner. I plugged everything into that (FM9 and the FRFR) this time. My guitar wireless input gain is set at -16, which I think had a major impact because I experienced almost no noise with the same settings. I had to drop the threshold on the input 1 gate significantly to get the same noise. When switching to a clean or crunch amp, the noise was not present, even with no additional gating.
Also - I went ahead and followed the steps
@strabes mentioned (thank you for that), and everything pointed to EMI like he said. I had one situation where my FM9 was buzzing with a cable plugged into the input jack from the patch bay, but no guitar plugged into the patch bay input. Most likely user error or a glitch. Seemed odd though. I have not been able to reproduce that since. I rebooted the FM9 and it seemed to go away.
To sum everything up, I think I have a combination of "some" dirty power, amp gain and noisy guitars. So the proper solution seems to be to utilize the tools available to alleviate the noise and shape the tone so it's less harsh. The BritAFS100 2 is my favorite FAS model, but I recognize it is a very harsh amp, even at low gain settings. For example, I use it with the gain on 3.25, and the MV set to 6.
After doing some testing today, I think I have found a happy medium. I ditched any gate blocks I was using and now just use the input gate. I have it set to a threshold of -55 and a ratio of 2.5. I've also dropped the input trim of the amp to 0.895, as my main LP has very hot pickups. I got pretty obsessive about this situation and I was afraid that I might have something wrong with the FM9. I don't think that's the case. I think it's a situation where I didn't do a lot of gig level testing at home and it turned out that there's some noise there. I also think my pickups are pretty damned hot and I am getting some EMI/RFI whether it be at home or at a venue.
My path forward is to add copper shielding to both cavities on each guitar and be conscientious about gain levels and settings. Hopefully things will be better at my next show. I'm going to keep an eye on things and if I encounter more weirdness I'll report back.
Thank you to everyone who chimed in on this thread with your suggestions and advice. Much appreciated.
