That's almost certainly what it is. Perhaps not from the window heat. But the 'buzz' you get from inductive pickup would be a whine on an aircraft since it is a multiple of 400 Hz rather than the more familiar 50/60 Hz buzz. Window heat is particularly bad if it is a 'chopped' waveform when it is not on 100%.
Here's an idea (cheap and non-destructive):
Touch'n'oops, obtain one or two split ferrite core filters. The kind that can be snapped over a cable. Like this:
Snap one over the mic cable (before the adapter) or one on each cable (mic and headphone). Once through is good, a couple of wraps is better (like the photo) if length is available.