I have an optima mk3 into a dx500. I'm happy with the way it is running with the a99. I just turn the stereo off and the problem is solved. I have talked to all the neighbors near me, and they say they haven't noticed a thing.I have not seen any information posted about what type radio or power level you have?
If the radio is super whack packed top gun modulated then could be spurious RF SPLATTER being transmitted.
I have used A99 verticals and never had any problems with RFI,,choke wrapped on the coax at fed point and clean modulation from the rig,