2003 Chevy Venture frustrated with 2003 Venture van I just

The van is a 2003 model chevy venture van with 90 K miles on it. It was a repo and was purchased off of a local dealer it had been serviced and told that everything was perfect. We've had it a week with no problems at all in its running/driving. A few days ago I noticed that the fan belt is starting to make a noise and we need a new belt. (No biggie)

BUT

this morning I went out to start it and it wouldnt start. I turned the key and all the lights in the dash came on everything is bright and working. But when I went to crank it over there was NOTHING no cranking no noise NOTHING complete silence.
I got my husband to come out and try and again the same thing happened. Well about 15-20 minutes later I went out to try and start it with the overhead lights on (to see if they went dim to rule out battery) and it started perfectly. Only noise I could hear was from the belt

we drove to get the battery tested and found that the hot wire going to the fuse box (ontop of battery) was VERY loose so we tightened it up and drove to pick the kids up and home IT DROVE and started PERFECT.

ive been home a few hours now and its killed me worrying about it so I went to try it again and its still starting perfectly but now there is this noise coming from the driver side somewhere it makes the noise a few seconds after its started then stops. I dont know how to describe the noise its like a low rattling or something.

i went back out to try and record the noise for my hubby (he dont believe me) and it didnt do it but 15 min later when I went to move the van it did the rattle again and this time did it longer before stopping

here is the only things we have done to the van since buying it.

1) The dvd player wasnt working after being told it did work so the guy we bought it off of said he would fix it for us. So we drove it to a car audio place and they removed to old dvd player but havent put the new one in it yet so as of right now there is no dvd player (THIS WAS DONE 2 DAYS AGO)

2) we ordered 2 keyless entry remotes for it because without the keyless entry we had to put the key in to get all the doors to come unlocked. Now that we have the remotes its been great

3) We had an extra key made for it at walmart

other than that. We havent done a thing to it.