I took a drive a week ago and went off road for a gentle 3 minutes. Now back at home there is a manure smell in the cab that "blossoms" when the Avalanche is parked for an hour or longer. I can open windows to get ride of the smell, but upon parking, the smell returns. I tried an under frame car wash and that didn't solve it. Suggestions?

2003 Avalanche 1500

 

Trying to delete this post but cant see how. I found a gallon of old milk under the back seat. Sick!

 

ha that's a bad surprise