So is the Garmin's squelch actually opening up (ie, you're getting an RX indication on its display)? If you turn off the G430, do you still hear noise in the intercom?
If squelch is opening actually opening up, the following are some suggestions and troubleshooting steps you can go through:
First, understand that RF interference is the function of the entire aircraft wiring design and not solely individual components. In SkyView's case, we performed tests at a fully certified lab that Boeing (we're in the Seattle area) also uses. SkyView meets/exceeds RTCA DO-160F, category H, for aviation COMM, NAV, and GPS bands. Cat H is the hardest to pass, for devices that are in direct view of an antenna. We did our tests with a full SkyView network with long cables, modules, servos, GPS antenna, battery, etc. You may find that the display by itself is "quieter" than a whole network if you disconnect the display from the SkyView Network modules, but the whole network does pass including all accessories and wiring, all of which can have effects on emmissions and interactions with other products like radios.
Even certification requirements do allow some noise output. No electronics are silent, and the standards do have noise limits. This is why you will see may see squelch level differences when you have a SkyView on vs. off. We're by no means claiming it does not output RF noise at all.
RF interference can be a hard issue to track, and wiring configuration, antenna location, antenna ground-plane, and general dimensions and construction materials of the airplane can make a big difference. Even manufacturers of certified planes struggle with these problems.
Next, a few suggestions:
The first thing we would recommend trying would be to install a 50 ohm load on the radio, right at the back of the radio, instead of any antenna or coax. This should block all RF from the radio, but the radio will still draw power and create RF inside. Do you still get the noise? If so, the radio's shielding isn't ideal. If you no longer get the noise, try the dummy load in place of the antenna to test if it's getting in the coax.
Next, if that fixes it, then put the 50 ohm load at the end of the coax where the antenna goes. Does the problem come back?
Knowing these things will help isolate where the RF is getting out of the system and into the radio.
Most noise comes from the power input. If you have a SkyView backup battery, does it happen when it's running on battery and not master (pull the circuit breaker/fuse for the EFIS)?
Is it the network cables? Does it do it when they are all unplugged from the screen?
Note that just moving the antenna isn't likely to help unless it's really close to the SkyView or components.
