My Nike Air Maxes randomly inflated?

Today, I was at the Indy 500 wearing my 2009 white Nike air maxes. I stopped for about 10 seconds and then started walking again and noticed that my heel felt like I had stepped in gum. When I looked, there was no gum and the heel of my shoe was actually inflated. There is literally a circular bump that sticks out of the bottom of my shoe. It's uncomfortable and it only happened on my left shoe. The right is still fine. I didn't abuse my shoes at all or anything of the sort and this is my first pair of Air Maxes ever. I know that heat expands air, but it wasn't that hot and as I said, the right shoe is fine. There also aren't any noticeable holes in the shoe. What do I do? Is there a way to pop it? I don't want to have the sound every time I step of air inflating and deflating. Can I return them? I bought them at Christmas time from finish line on the clearance rack, but I don't have a receipt. What is the cheapest and easiest way to fix them without buying new shoes? Thanks for all help.