03 Mazda 6 rattling when accelerating?

I have a 2003 mazda 6 and it started making a rattling noise when I step on the gas. Initially, if I took my foot off the gas, it would stop and I could step on the gas without issue. Over the past week or so of driving it and trying to figure out what it is, it has only gotten worse. Now it has gotten pretty loud and is continuous while I step on the gas and continues, but slows down and eventually stops when I let off of the gas. Does anyone have any ideas about what it could be?