does it feel like it is going over the notches? even on newer wheels (my mx310 compared to my old mx300) where you dont hear it so much, you can still feel it going over notches. anyway, each time it goes over a notch, it clicks a button inside..... really theres 4 buttons instead of 2, and they are the exact same buttons. if its a mechanical problem its not that hard to fix.
anyway it depends on the type of mouse where this is concerned. aking apart my mx300 didnt void the warranty when it broke (electric shock, there was no saving it anyway). i also took apart a warranty-less standard logitech optical, but none of that mattered cause i fixed it. but when i got my 310 replacement for the 300, i noticed that they have no screw hole in the bottom, but in the labels there are + shaped perforations, presumably there are screw holes underneath, so to open it up i would have to break the label.
anyway if its a Logitech MX you still have your 5 year warranty.