I have a 2012 Rubi with about 5400 miles on it. I have a strange noise that is happening when I shift into 3rd. Let me see if I can describe it.

Starting from a stop, start in 1st, 2nd, and then shift into 3rd. After shifting into 3rd, about 3-5 second delay I hear a clunk/pop. Almost sounds like play or backlash in the drive train. The only weird thing is I'm already on the gas and the clutch is out. Doesn't do it in any other gears. I can't really tell if it is coming from the front or the rear. It almost sounds like a backfire sometimes too.
Anyone else have an issue like this?