Ferittes in place with same noise. Only happens with battery in place and charging. It's a squeaky dirty noise. If the plug to cig lighter is moved a bit the noise gets disturbed. I've heard this type noise before, sometime in my life. I suppose it's an interferece of some sort. When I key the mic it completely disappears for 2 seconds but gradually comes back up to original volume. I'll look at shining up the inner barrel of cig socket. If this don't help I'll just keep the bat out of the circuit until needed and runs fly off ships power(unhandy for I normally fly within minutes of starting and will add to my ground time) or run off bat and keep charger unplugged until needed. Either way is an inconvenience and potentially dangerous (fooling around with this as a distraction to flight)