Dodge Repair: Mysterious Battery Drainage, perfect shape, battery place

Question
I am having trouble with my battery losing power if the car is left undriven for a couple of days.  It's a 99 Avenger that I recently purchased.

Some history on the problem:

I recently had the alternator belt replaced; it was badly shot and it squealed quite a bit.  The mechanic told me that he had problems with the battery when he first tried to start the car, and he told me the bad belt was most likely the problem.  After the belt was replaced, I brought it home and the next morning the battery was out again.  So I charged it, thinking it was just too low in the first place.  It lasted a week on the charged battery.  After 1.5 days of not driving the car, the battery was out again.  I had the battery, alternator, voltage regulator, etc. checked at Auto Zone.  They told me everything was in perfect shape.  I had heard just a little squealing one day, so I took it back to the mechanic, thinking that maybe the belt was put on too loose.  He checked it and it was very tight and he even ran the same tests and came up with the same results.  He told me that there must be a light staying on somewhere and that I should look in the car when it's dark to see if there's anything I could see.  I just did, and everything is completely dark.  I couldn't find a light on anywhere inside, including the trunk and under the hood.  I don't have a latch on my glove compartment right now, and it's hanging down, but there are no lights on.

I do hear a slight spark sound sometimes when I start the car, but I'm not sure what would be causing it or if it has anything to do with my battery being drained.

What in the world could be draining my battery overnight?

Answer
if u drive it to some place and have the battery tested it will always pass  U have a surface charge on it. A battery place will have a better tester to put a load on it and see how many CCA is in it  most of the auto places will have only a voltage checker and not a load devise to load down the batt with nothing on. IF it passes then  U can take it to a good electrical guy and have him do a battery off draw test and see what computer  circuit is staying on with the key off.