MP3s sound muffled on car stereo?

[peggypwr1]

Hello, I burned a bunch of MP3s to disc for my sis's car. She has a Sony CD/MP3/WMA player, about 6 months old. For some reason the majority of the MP3s, sound "muffled". She really has to turn the volume up to hear them.

On the computer the MP3s sound fine and clear. Is the Sony at fault?

I hear that WMAs are actually better, if I re-encode the MP3s in WMA will it make a difference? Thanks for your time.

[MOVIEGEEK]

Use MP3Gain to normalize the MP3's but try WMA from the original CD's,converting MP3 to WMA will probably sound worse.
BTW:this topic should be in the Audio section.