Just changed the oil and the old oil looked normal. Haven't really checked the antifreeze yet. It sounds kinda like it's coming from the drivers side but it's hard to say. Tomorrow I'll pull the belts just to be sure. The car runs fine and seems to have plenty of power as usual. I was told it could be the spark knock from bad gas or since it still has the original plugs/wires. Also was told it could be the flex plate, but wouldn't a flex plate rattle all the time instead of just accelerating in drive?