So I just got my first roadbike (K2 Mach 2) with Shimano Tiagra components and Shimano 105 rear derailleur. Everything seems decent about the bike especially for the price that I got it ($465 discounted from $800). My only thing is that the rear derailler is not exactly centred over the casette so that when I shift in the rear, the chain will jump and engage etc. but it will make a small ticking noise as the chain comes off of the rear deariller and onto the casette. Should I be bothered to try and adjust the little screw somewhere in there or just leave it be? If so where is that little screw?
You should adust it, of course. There might be two screws. Certainly there is one where the derailleur cable enters the the rear derailleur. The nut surrounds the cable. The second one might be at the cable stop on the top tube. Same thing there. Check the Park Tool website for details. Good luck.
don't mess with the two little screws unless the derailleur throws the chain of the cassette. experiment with the "barrel adjuster" (the nut surrounding the cable entering the derailleur) so you can learn and understand the changes that cable tension makes. Learn a little about it now and you'll be able to adjust any derailleur.