I just experienced the same symptom while in Nashville last week for biz, and it was annoying enough that I had to find a shop and deal with it. So I pulled into Bike Pedlars, whose tech Andrew told me he hears that symptom described a lot, and it's almost always the pedals. Then he sold me some pedals, and off I went. Props for great service to Bike Pedlars.

You can slap on some pedals off of another bike to check it out real quick.