Bicycle Mechanics - clicking (strange, I know)

I've got a brand new Trek 2100 that I've put about 500 miles on, and I lubed the chain today and took it out for a ride but it started making a strange clicking sound and it only made the sound in one specific gear. One of my biking friends said the rear derailleur may be slightly misaligned which is causing the chain to slightly miss the rear cog (that it makes the sound in), which is making the click. any ideas?

Is the sound coming from the front or rear derailleur, and what gears are you in when the clicking occurs? (i.e. big front, second to smallest in rear)

Could be miss alignment of either derailleur, crosschaining etc.

Most likely your friend is right. Shift cables often stretch (actually, I think that the outer housing seats a little bit) on relatively new bikes and screws up the derailleur adjustment ever-so-slightly. If that's the case, turning the barrel adjuster by the derailleur 1/4 turn counterclockwise will fix it.

On the other hand, there's this to consider:

When you bought your bike, remember how the sales person waxed on about their wonderful service and the free tune up they provide after your bike is broken in? Well, your bike is broken in now so you should take them up on their offer. Other stuff happens to new bikes, crank arm bolt torque and headset adjustment for two can result in expensive repairs if they aren't checked. I've never understood why so many people fail to take advantage of the service that they paid for when they bought the bike.

thank you very much! We turned the barrel adjustor just a little bit and it got everything lined back up. I've actually taken my bike in to get tuned up twice already because it's not even a month old yet and I figured things were settling. I plan on taking it in again in a few days just because it's free and definitely worth the time.

thank you very much! We turned the barrel adjustor just a little bit and it got everything lined back up. I've actually taken my bike in to get tuned up twice already because it's not even a month old yet and I figured things were settling. I plan on taking it in again in a few days just because it's free and definitely worth the time.

I think you're going a little overboard on the free adjustment policy here... typically I only need to service my bike every few thousand miles, and then its typically a quarter turn of the barrel adjusters, bring in the brakes a bit and true the wheels and thats about it...