Noise from HAI Voice Module Audio Out Headphone Jack

I've installed a Two Way Voice Module and at first it was working perfectly, but recently I have found that there is a lot of noise coming from it whenever it plays any audio or if the phone intercom is used. Its similar to a cell phone interference buzzing sound that goes on and off and is very annoying. There is no cell phone near the HAI controller/voice module. I've tested with headphones plugged into the jack and the noise is still there. I've tried moving wires around and removing the voice module board and moving it a bit further from the other wires and the voice was still there. I've also tried power cycling the controller to no avail. Its a Rev C board with the trigger+headphone jack. No mic or speakers connected, just wired up to a NuVo Essentia (or headphones in this case).

Any ideas? Is it a bad board? I'm confused because it seemed to work without interference before, but nothing has really changed around it and I've tried powering off all near by electronics and it makes no difference.

The sound buzzes slowly first (low hz), then buzzes quickly then slowly then stops for a bit then repeats.

Has anything changed with power? UPS, the unit itself?

Nope, also tried unplugging the HAI controller (so that it runs off battery) and that made no difference either

Did you find a solution to this?  I am having the same issue with noise on the two way voice module.

I realize this is an old thread but just to chime in my input for others who experience this problem, it is some kind of interference issue that happens on some of the Omni main boards themselves.  If you power cycle your Omni board and then produce a sound test within the first 5 minutes of boot up it will be crystal clear (at least in my case) and then after about 5 minutes, the exact noise as described above starts up, first quietly and then within 10 minutes it will be full blown and drown out the audio itself.  I had my audio board replaced and it had no effect which means the problem is coming from the Omni board which I did not feel like pulling out and replacing.  Instead, i picked up a noise filter (designed for car audio systems to eliminate a ground loop), unfortunately it is not 100% as these devices are designed to eliminate a ground loop and thats not the problem in this case, however it does cut out the background noise significantly so at least you can make out what the audio board is communicating once again and less chance it will damage your speakers if you are routing through an amplifier like the HIFI system.  There will likely never be a real solution to this problem, this was the best I could come up with.  Would love to know if anybody out there actually figures out the source and is able to neutralize it.