I just hooked up a sony s2000 hu and 4 pioneer 4-way 6x8's in my friends '89 thunderbird and now there is some noise that comes out of the speakers, like interference noise when you have the volume down to 1 or 2. the car has premium sound if that makes a difference. the sound goes away though after you turn it up past 5 but it does it with whatever you are doing. at first i thought it was just bad reception from the antenna but i put a cd in and it still does it. any help would be greatly appreciated.

thanks, mike