This is like posing a question to a lawyer: "It depends."

What might be helpful to non-experts is a typical step-by-step
approach to identifying the type and source of interference and then
addressing it. For you AI types (is that term still used?), an expert
system flow chart. EX: If it's a noise in the radio speaker, go to
step 2a. If it's a noise in the audio vario speaker, go to step 2b. If
it's a disturbance in the needle or indicator of an instrument, go to
step 2c. Etc. "It depends" covers too much ground.

I've chased interference before, the most maddening case being hearing
a French African channel on Voice of America non-stop thru the
aircraft radio years ago when flying at Caesar Creek, OH. It was my
brother's glider, actually, but we worked on it together. From memory:
capacitors, homemade high-pass, low-pass, and band-pass filters,
shieded cables, shielding around various components, etc. Eventually
we drove the trailer over to the VOA facility, parked on the road
outside, pulled the fuselage out, and started working. That got action
pretty fast. I didn't realize VOA had security guards. Once they
believed our story, and that the Komet trailer wasn't full of
explosives, we were actually invited in to meet the manager and get
info on freqs, antennas, power, etc. Pretty awesome numbers, as I
recall. I honestly can't remember what finally did the trick. Maybe it
was my brother moving to VA.

Chip Bearden
ASW 24 "JB"
U.S.A.