Stock Stereo making CRACKING sound

[MsRaphy]

I got into an accident back in January on my birthday.. A car hit me from the back which bent in my body frame and made the trunk unable to close.. It's finally got repaired after two months in the shop.. After the accident I noticed there were some cracking sound in the stereo if i am playing the CDs and when I raise the volume over 30 or 40.. the volume is messed up at number 62 (MAX) sound like it is in the volume range 30. After getting my car back, it got worse and it does the same thing when I plug in my iPhone as well.. I don't know how to fix it at all or know what going on with it.. I would like to also include that I did have a 12 inches speaker in the back with my amp.. Before I went somewhere for my birthday, I took out the speaker in the trunk because it won't stop moving around (It wasn't nail in yet) I was so glad the speaker wasnt there when i got into the accident thou.. PLEASE if someone know what to do please please help me.. I drive from PA to NYC every weekend (2 hours drive)and it suck not being able to hear music anymore