Das Ist Bomb

I recently bought a 98 Audi A4 1.8t and I'm loving it, but a few things are really bothering me.

First of all the car radio works perfectly fine, but I had to change the battery and ever since then when I hit "mode" to switch it to the CD player it completely skips the CD part as if it where never there. It just goes to tape and then back to FM. I checked the CD changer in the trunk and its working completely fine I just don't know what's going on. Also as of late whenever my car gets to higher temperatures or I shift gears badly my car starts to rattle, I was thinking it was the turbo but the person I bought it from said he put in a new turbo?

If anyone can answer these questions I'd love them cause no CD means no blasting music, no blasting music during the summer=unhappy camper because I have to listen to the girlfriend lol