Exhaust noise?

[RyojiKaji]

Tonight I went to the mountains for some driving. On the way back I noticed that my car sounded different. When I let off the gas in any gear at any speed there is a noise coming from the rear. I tried it while I was parked and out of gear. It sounds like I put a hole in my exhaust somewhere. I'm not sure if it matters but I was driving in snow part of the time. It sounds kind of like a weed whaker. The sound is not there when I'm out of gear and Idiling. The car drives the same it just sounds different. Any ideas?

Thanks in advance.