My new IC-R6 sounds very "harsh" on the aircraft bands (It doesn't sound this way on local police frequencies.) I've tried setting the AF Filter to "On", but when I go to scan my preset aircraft frequencies it resets to "Off." I'm 4 miles from my local airport: KGRB, Green Bay, WI; the signals are relatively strong on the RF Meter and I have a Diamond SRH77CA antenna which is supposed to be one of the best for aircraft frequencies. Can anyone offer any advice, please?