White Noise through Speakers?

[pointedstarman]

Looking for a little advice rregarding a fault that causes 'white noise' to build up such that what starts as a little crackling ends up, after about 20-30 secs, drowning out whatever is being played through the speakers. The fault occurs when using any of the inputs (fm/am/dab radio, cd or aux) and changing inputs has no effect. The fault is cleared by switching the stereo off then back on again.

The car is a 2007 E65. Local BMW dealer thinks it may be a software problem and wants £99 to do a recode and it's not covered (they say) by the AUC Warranty?

Any help / info on similar experiences greatly appreciated.