1996 Ford Mustang 2 problems

Noises problem
1996 Ford Mustang 6 cyl Two Wheel Drive Automatic

I just purchased this 96 with 92 K miles - seems pretty sweet in and out but:

on the first tank fill up it leaked a bit out of one of the tank vents - now at less than 3/4 tank it seems to have stopped ---- can I just get a plastic tank repair kit and close up that vent completely?

also, there is a whining//humming noise at the passenger side rear underneath of car when you start it up - almost electrical or something - any ideas?

thanks

RR