Since the purchase of my cub this past spring, I too had been having extremely random radio static problems that didn't seem to correlate much with any one constant. Sometimes certain frequencies on my comms would be crystal clear, other days the same ground or tower frequency would be unbearable. Sometimes it would be a steady static noise, other days I would get pulses when the rear rotating (non-LED) beacon would pulse. Some days I could turn the beacon off temporarily and the noise would go away, other days turning that off wouldn't diminish the noise. Some days, I could turn the circuit breaker switch off for the electric turn and bank I have, and for a while that was the most consistent way to squash the noise, but then that seemed to have less of an effect. Didn't seem to be temp based or RPM based. Again, very very random and no constants that I could find to create the problem or solve it consistently. On the ground everything was crystal clear, after start up and flying things would get noisy.
As everyone says, check the grounds. I began doing that from tail to tip. First cleaning and ensuring the beacon ground was good.. Tracking wires forward. Check grounds and the wire situation under the wing root panels where my light switches are located, under the seat at my battery, grounded the engine block to the firewall stud as few suggest on here, etc.. Further following wires up to and behind the panel. Separated power wires and routed things further away from audio lines if I could. Outside of grounds we ensured that the VHF radio and antennae were working well enough, and that there was not a ground plane issue. The old Narco 810+ that was in my bird failed at the beginning of August (after take off transmit failed to work, but could receive.. a bench test proved transmit circuits were toast) and was replaced by a Icomm A220.. When having that installed I had hoped that perhaps the radio itself had some internal circuitry that was injecting some sort of interference, but no luck. The static was still there.
I knew it was something with the radio (not in the intercom), the turn and bank, and then one day discovered turning off the engine gauge also made static things silent.. And it turned out turning off the UMA 2 in 1 engine oil pressure and temp sensor gauge seemed to be the ticket. But unlike turning off the turn and bank, not too keen on flying without seeing what the engine oil is doing of course. I had a new connector put on the gauge as the soldering looked like it could have been suspect and also ran the oil temp/psi sender lines through a different hole in the firewall, away from power wires which they had been sharing another hole with. Both didn't solve anything.
So long story short, I finally called UMA. They asked when the gauge was purchased (jun 2016), and immediately suggested I send it to them so they could install a new or better radio frequency filter within the gauge itself. I paid shipping both ways, they installed the new RF filter at no cost, and sent it back to me the same day they received it. First flight with the new filter, no noise. I didn't want to get too excited here as I had had temporary success in the past. Second flight, no noise!!
Thanks to badmdcnman's posts above and comments made about the UMA gauge, they turned me towards the idea that the noise could be that gauge. Happy to have found a solution after 5 months. And if anyone else tells me to 'check the grounds' once more...