2006 Lincoln Zephyr noise issue

ok, need some ideas here guys. worked on a zephyr several months ago and put in an amp on subs and seperate amp on the factory speakers off of the factory indash stereo. the problem i am having is that the vehicle was getting a weird "hiss" out of all the speakers (front/rear mids AND front tweeters -- all factory speakers). this hiss is only noticed if the volume on the radio is completely off and then it was very faint. i re-adjusted the 4 channel amp and managed to get the hiss out of the mid-range speakers but couldn't get the tweeters to stop hissing. i realize that the tweeter is more prone to hiss because of the frequency tweeters are designed for but just for giggles i attempted to put bass blocker (caps) inline to eliminate the problem to no avail. i also tried tuning the inline converters down and that didn't help. i also tested for a bad inline converter and/or bad patch cords and all are fine. at this point i broke down in tears and ran around the shop naked until i was sent home sick -- lol j/k. i also tried manually grounded the radio to see if there was noise getting in thru a ground loop and no such luck. also tried using a ground loop isolator and that didn't help any either. btw, this hiss isn't like engine noise where it moves up and down with engine reving and isn't static. i really hope someone else has an idea because i'm fresh out. thanks in advance for the help and i await a response.

Just put a Sony unit in my 2001 Lincoln LS using the Metra kit.  Very clean looking install - meshes real nice with the factory dash plastics.