Save yourself the trouble, go to your nearest "dick smith" type store, somewhere that works with computers, and buy a bout 5 Ferrite(sp) resistors, these are the black lumps on all your computer cables, should cost about $2 each, put them on every wire in and out of the radio, they just clip around the wires,,, should be problem fixed.
Took me about 18 months of taking radios out sending them away, only to be told nothing wrong with them, i was having massive mic feed back, the easiest cheapest fix i ever did find, i put them on every radio i fit now, even they dont need them.
PS i have nothing to do with Dick Smith stores, or any computer store that sells this product.