Adam745 - I have got this problem fixed by performing some wierd steps and you can give it a try:
- remove the radio/cd fuse (usually fuse no. 76) while the car engine is turned off
- eject the CD changer box (where the CDs are inserted) from dashboard
- plug-in the fuse again
- start the car and play a CD from main CD player (it should not make that noise and should not trip to radio)
- once you check the noise is not coming after playing the CD for 5 mins or so, insert the CD changer box with CDs
- run any CD from changer now and it should work fine
I know thats wierd but it worked for me, all the best !!