I just picked up my new Trek 7.3 FX today. They spent a good amount of time tuning it up and installing my bike computer before they did the final fitting and sent me home. I did ride the bike at the store but didn't get into the 8th gear any.

When I went for a spin around the neighborhood I noticed that whenever I'm in the 8th gear on the back (sorry I'm not familiar with all the bike terminology) that the chain is rubbing in like 3 - 4 different spots on the metal guard/guide. It happens in all 3 of the big gears whenever I'm in the 8th gear in the back and makes quite a bit of noise.

My LBS closed at 7 so I'm just trying to get some info on what could possibly be the problem. I'm sure if I call them tomorrow I can take the bike back in to get the problem fixed, but hopefully you all can ease my mind. I don't want this to be a serious problem since they already installed my bike computer.