Loud "pop" noise coming from deck

I've had my simplicity lawn tractor for about a year, bought it used and never had an issue with it. This year I take it out to mow for the first time and I'm occasionally getting a loud "pop" noise that seems to be coming from the deck. When driving, it makes this pop noise about once every 2 or 3 minutes. It does this weather the blades are running or not. it almost seems like something is binding up, then releasing. Under visual inspection, everything looks fine. Any ideas? I have the hydro 14 model

Edit: I just took the deck off and drove around as a test. It still makes the pop noise. I'm assuming this is something with the "transmission" then. Is this a common issue with a known fix?

,You may have resolved your problem by now, but if you have not, here is some information. I logged into simplicity's homepage and found the following; your simplicity hydro 14 is a Regent model 1693080 or 1693082 with a Tuff Torq K-56 transmission. An illustrated parts breakdown is shown with all parts as well as part numbers. This would be my last resort unless your absolutely sure the loud pop noise is coming from inside the transmission. After removing deck and disconnecting negative cable from battery, wheels scotched and park brake on, I would make a thorough inspection from underneath tractor with a flashlight. Check out rear wheels also, Simplicity recommends pulling rear wheels and applying anti- seize compound to axle shaft. This should be done at production factory, but who knows, maybe they're applying it now. For personal safety always use jack stands when pulling wheels, I pull one wheel at a time. Let us hear from you and what the culprit is. Mark