there is a a guide somewhere if i remember but it is simple you need 4 keys to take it out,
you can buy them off ebay for a couple of quid
http://www.ebay.co.uk/itm/CT22AU01-A...#ht_2126wt_932
you need 4 to be honest
i had the same problem and it was the earth cable on the back of the unit the way to see if it is the earth without removal is start the car switch to AV on the tv and turn the volume up on the stereo and go for a drive take it through the revs and it it makes a supercharger kind of noise then that is due to the earth on the back of the RNS-C
i plugged it back in and snipped the Gala feed while i was there to get TV in motion
you can just go to halfords and ask them kindly to pop the keys in for you they were more than happy to do it for me