yeah, when i took out my radio to put in the premium unit (which rocks), i noticed it had some kind of rubber non-slide padding on the bottom of the radio space. i guess this is to really prevent the radio from jostling any when driving or something. mine was a little torn and old, i guess the previous radio had been messed with before (i didnt have the codes either but didnt need them when i traded it in for the premium unit). if you're radio's never been removed, it may be harder to get it pulled out. im not saying pull it hard enough to feel like you might hurt it, just posting an observation that could help. good luck!
~ delic