Reviving an old thread, but, it fits my problem...
I recently completed a panel upgrade in my RV-8 which included replacing my 496 with a Aera 660. The rest of the panel is dual G5s, GNX375 plus GMC507 autopilot system. The original 496 was mounted to the panel in a Gizmo mount with hard wire connections and was quiet as a mouse, no interference noise at all. Not so with the Aera 660, it's noisy! It's also mounted to the panel using the bare wire connections; it took a few minutes of detective work to narrow it down to the 660, but once I figured that out, then to determine, what's the source? Power, audio or RS232 data?
I'm using both of the 660's 232 data ports to the G5s and the 375; I switched off the ports but the noise remained. Yesterday while in the hangar I disconnected the 660 audio feed to the audio panel... aha! Silence! I was happy up until I started the engine and the noise was back, although a lesser amount. Well, cr@p! So it's not the 232 data (or is it?) and the audio is disconnected, so what's left? Power. The noise does rise/fall with RPM, so, alternator power noise I guess? And how the heck do I fix it? The bare wire connector was cut fairly short in my install since the -8 has a compact panel; there is shielding in the connector but I only used about 6" of that wire before opening it up to tie into the the 232 and power leads. So, anyone else run into this and how to fix it?
I noticed an older thread from 2012 with similar issues on the 796.
http://www.vansairforce.com/community/showthread.php?t=87737&highlight=796+noise
Garmin, if you're watching, why so noisy? How do we fix it??