Is it about a 1 cycle per second ticking noise? When you push a button or twist one of the selector knobs on the Trig control head, does the ticking cycle start over, or tick faster for a short while? If so, I bet it's the same noise I was trying to track down in my install.
With absolutely nothing else connected anywhere in the plane - electrical system rewired from scratch, using the Trig internal intercom - I heard a ticking noise, about 1 cycle per second on the output of the Trig. After some experimentation, I found I could get the ticking to change by fiddling with the buttons and knobs. This suggested to me that it was something to do with the interface between the control head and the radio. I then discovered I could get it to stop entirely by disconnecting one of the TMAP lines going between the control head and the radio unit. According to one of their install documents, TMAP is the RS485-based serial protocol the control head and radio unit use to communicate. My guess is that there is a 1 Hz update/polling clock as part of the system design, and there's a design flaw somewhere that's allowing the serial data communication itself or that clock signal to leak into the intercom audio path.
So, what to do about it? I seem to remember trying various shielding options for the TMAP lines, but that didn't do anything. Then I found some references to
firmware updates for noisy radios on their website, so I sent the control head and radio to Mid-Continent (Trig's US service center) and had them update both. I think this was covered under warranty, but probably had to pay shipping both ways. I can't remember if the updates made a noticeable difference, but I know it didn't make it any worse.
Finally I tweaked levels on the radio/intercom and headset so that the noise was minimized, just as txpacer suggests above. It's probably still there if I try to hear it, but it's not too noticeable with the engine running. I put on about 150 hours since May and I haven't given it much thought since then.
Curious to know if others can reproduce the change in behavior with the knob twisting and button pushes.
