Yes, playin cards or something else similar. The front left is slightly off balance due to how they put those lil cushions. When the disc drive is running, the vibration in that corner hits the surface of the table, stand etc and causes the loud noise. I've had this happen and was perplexed until I found out the reason online. Try my method and you'll be relieved like I was.
Thanks Lik I'll try it tonight and report back!