It sounds like you've got the newer Shadow style derailleur. I have personally found this design to be more difficult to tune, with the traditional style more forgiving as you describe. Most noticeable with the Shadow design is the higher chain tension, which seems to generate more noise, at least in my case. In addition, shifting wasn't as smooth. I "downgraded" one of my bikes which came with an RD-M3000 (Acera level Shadow) to an RD-M360 (older Acera design) and it's much more pleasant to ride.