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Sounds like you are describing something fairly common with the Harman Kardon head unit. It probably has a broken circuit board due to vibration and some bolts that are too big. It can be repaired by taking it out and sending it to Iron Cross.
+1 Way too common! That exact problem is what makes guys go to aftermarket. Same thing happened to both of my HK's when I had em. Pissed me off to no end. Iron Cross is great at fixing it though.