Originally Posted by mcjimbosandwich

i must be going blind. didn't see that you live in nyc. anyways, the reason why i suspect this was the following

I rarely clean my cassettes, and when i had to get a new chain, i decided to do some cleaning. this was when i realized that the dropout as well as the cassette body were lose, and consequently, the derailleur settings were based off of a lose drop-out, with the B-screw setting messed up as a result. However, I didn't realize the consequence of this and just tightened the cassette, but my bike on the stand to adjusted the RD. It shifted fine, but with a clicking noise. I slowly turned the crank to see where it's from and realized that it happens when the chain goes from the top pulley to the cog, it was actually hitting an inner cog, thus causing the clicking; it also happened that the spacing btwn the pulley wheel & cog was way to far. A few turns of the B-screw did the trick.