Ancient aeronautical engineer here, with some radio-amateur and electronic background.
Quoting
hangflyer's original post.
Originally Posted by
hangflyer
There is an intermittent white noise that only appears on VHF (ADF is clean) that reduces a received radio transmission to 2's or 3's, however it is extremely directional and ... only happens if .... only happens when the engine RPMs are above 2200. There is no noise at 2150rpm and then at 2200rpm it is there in full intensity, it does not increase in any way (pitch/strength) as RPMs increase.
....the white noise kicks in on the radio. The noise does not change with pitch, it is not a whine, it does not get stronger or change frequency. It is just white noise.
I'll admit immediately that I'm totally baffled by the description of the noise as "white noise", i.e., a "hiss".
With just about anything 'vibrating' (bonding, etc.), I would expect the interference itself being "modulated" by the vibration source, be it propellor, ignition, airframe vibration, or whatever.
From
hangflyer's description, this is not the case.
But I would say
MurphyWasRight has a point, it's not RFI "as such".
If so, it would also show up on the NAV radios, which are roughly the same fresuency band.
A recording of the noise might help, as suggested before. Somebody might recognise it as something familiar.
CJ