Rev related radio whine just started - causes?

[hut49]

Having had reasonable radio reception (as good as it gets anyway, in a GRP tub) I've suddenly got a noticeable whine that is present at tick-over and increases in pitch as the revs increase. All stations affected. Nothing's been changed on the engine's electrics/electronics. Normally I can't the radio over the engine and exhaust but now I've noticed it it's got to stop. Any ideas?

[mongoose]

Sounds like you could do with a surpressor on your alternator.Cheap as chips from Halfords and the like,and a doddle to fit too