do you have a water spayer for the rear? it can leak from there. it's also one of the trouble spots. i just completely removed mine. and yes it can come from uderneath. the gas tank area is prone to rust for EF's in general. man i wish i had pictures of my EF before and after pictures. just getting my car resprayed after about 300 hours of body work. hey i paid $100 for a clear titles 91 si, so i feel i came out on top. just the rust... WAS BAD!