What year model Range Rover, what type radio did you install, OEM or Factory? At a guess you may have added an amped radio to an already amped system. You'd need to remove the amps out of the circuit in the doors...depend on the year model though.
For Land Rover stereo help and Ipod Auxiliary jack installs on most Land Rover OEM factory head units 1987 to 2004 check out Roverville - Radio Repair: www.roverville.us
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix in-car audio.