Man I have the exact opposit problem Mine will go way up and then when I try to turn it down it continues to go up. LoL, am going with an alpine to replace it.
speakers might be blown. Had a problem like that before in my mustang and it was the speakers. Just get an old speaker and hook it up real quick to see if that is the problem.
Aftermarket deck right? (almost all aftermarkets use a soft button for the volume control (providing it doesn't have a knob) they can wear out as they are just 2 soft metal pads). If it's the factory deck the knob it's self probably crapped out. ( $15 in parts, $25 to $50 in labor to fix. Might just want to scrap it or pick one up off ebay for $35 shipped.
It is aftermarket. And the remote buttons are soft and I use it ALOT. But I don't think it's worn down since I can still turn it down/up, it's just not loud. I can't find any speakers and I don't want to scratch something so I'll just have to take it to someone. Thanks for the help so far.
Update: Ok. Fixed! A very small AUX/LINE button was pushed in (on) causing it to direct the sound... elsewhere. :uh oh: