Please help....
 

I'm new to this site so I don't really know where to post this...
Either way, I have a 1995 Buick Regal Custom.
When I start the car, it spins but doesn't turn over. Electronics work fine and I got the battery tested and both the battery and alternator are completely fine.
When I turn the key back, I notice a buzzing electronic sound coming from the back of the car. It's alot like a spinning sound and it is not coming from the engine.
This usually only happens if we don't plug the car in on a cold day. But it's not cold at all and even after being plugged in, it still won't start.
It's probably not the starter since I hear a buzzing sound coming from around the back wheel area instead of ticking sound in the front. I have expended my only knowledge about cars from my time in automotives class. What do you think it could be?