Glad you got it resolved. I would monitor all functions of the vehicle to be sure nothing else is being interfered with due to possible RF interference. It might not be a bad idea, if necessary, to investigate adding a ferrite bead/choke to reduce outgoing interference from the amplifier.
http://computer.howstuffworks.com/question352.htm
Before being embedded into the cable, as shown in the above link, some manufacturers provided a clip-on version of the choke. I'm sure some of these are still available. I've tossed more of these than I can count
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2013 x35i (Space Gray, MSport, CW/CWII, DHP, Premium, Premium Sound, Technology, BMW-Apps)
Retired: '09 C300 4Matic, '09 GTI, '06 750i, '05 C55, '04 R32, '03 M5, '02 GTI, '01 M5, '00 M-Coupe, '00 540i/6, '99 M3 Coupe, '98 M3 Coupe, '96 328i,... '86 4000 CS Quattro... too many to list.