iFly GPS Forum

If it's a poping noise that varies with engine rpm, you might try turning off one and then the other mag to see it's coming from one particular mag. If so, look for a bad plug wire, P-Lead or Champion spark plug with a bad internal resistor (maybe several plugs). If it's a whining noise, it's probably your alternator and most likly a bad diode inside it.

For reference, my noise was static (hiss) in the headset. There was enough RFI that it was being picked up on the antenna and would break squelch on the radio.

All the suggestions of sources of the noise sound good to me. In my case with the new fuel flow meter, my noise was a periodic clicking sound and whine when powering the previously noise free intercom with aircraft accessory power. When operating the intercom on its internal battery there was no noise so probably one of those ground loop things. Unfortunately a coaxial magnetic choke on the intercom DC line like you showed didn't help me but wouldn't hurt to try. I squeezed a 1000 microfarad or so cap in the body of the Radio Shack three 12V jack box with some improvement. Eliminated the sound entirely by making and inserting an aprox 3000 microfarad inline mini coaxial power male to female jumper (about the size of an old 35 mm film container) right at the intercom. Easy for me to add the caps as were portable non-hardwired accessories.