ticking noise when I pedal

I'm new to the road bike...only a couple of months...and I noticed that my bike is suddenly making a ticking or clicking noise when I pedal. I took it to the shop I bought it, and the guy at the shop really knows his stuff and it's even stumped him! He took off the pedal, the gear, everything! Everything is tight and in place, but as soon as I get back on there's the TICK! What is it? It happens on the same spot when I pedal, and I know it's coming from somewhere in the pedal or gears.