e46 M3 Crackling!

[caterpillar]

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My 52 plate E46 M3 is fitted with the sat nav has a strange problem, the speakers on the right hand side of the car both work but at higher volume begin crackling until eventually they go off, whereas the ones on the left dont work at all when you balance the radio to the left hand side there is no noise what so ever (not even a crackle lol) any ideas? is this a common problem??

Thanks