ok more details about the situation.....i tried it with the sound off, it works ok but when i turn the a/c on aswell it tends to do sort of the same thing.....and also mind the fact i never replaced my alternator when i did a rebuild on my skyline so the alternator has done 184,XXX k's, but the motor has only done 60,000 since the rebuild.
my audio equipment,
dvd player in the front,
fusion 6inch splits and tweeters
pioneer 320w 6x9's
pioneer 1200w sub
pioneer 720w mono
its not a big system and my car has never done this in past only recently, the system has been in teh car for about a year now