When I'm in the highest (smallest) gear and pedaling hard, it sometimes "jumps". I'm not sure if that's the right word, but I feel a bump in my feet for a moment and then I continue pedaling. It feels like I'm shifting gears, but I'm not. I've spent some time today adjusting the rear derailleur, and all the other gears are good. Could this be caused by a worn out sprocket? I don't use this gear all that often, so I'm not sure why it would wear out faster than the others. Pedaling moderately is fine, this only happens when I push hard.
This is a 9-speed Shimano Sora.