I have a 2003 EXT with factory Navigation. About 3 months ago I got 7" screens installed in both sunvisors, and both headrests, as well as a DVD Player. I also had my subs and amp installed (Kicker 600.1 amp, 2 12" Comp-VR subs). Since the installation, the volume of my music will randomly increase and decrease. Not a slight change, but will drastically get louder and quieter. I thought it may be related to some SCV setting, but I can't find a SCV adjustment on the navigation system. Also, the the volume will change while I'm parked making me think it is unrelated to any SCV issues. Any thoughts??????