Yeah,
I knew I was going to get "Buy a new car" and "Install new stereo" .
But, your right I believe the sound is being made by the keyboards.
Morningdew,
Ok, now for something affordable.
It is likely that the offending frequency is just too dominant and it is masking the highs and mids.
If you have these files on a computer or can get your files onto a computer, download this tool.
http://www.har-bal.comLoad up your audio file into this program. It will analyze the file and give you a frequency trace of the amount of energy in the audio spectrum. Look for any sharp peaks (mountains) in the freq trace. If you have a lot of energy at 250hz it should show up in the trace. Follow the example tutorials to design an eq curve that will smooth out the audio. The idea is to gently reduce the peaks and perhaps boost the valleys so that the track is more listenable. This is too much to go into here, but they have good tutorials.
If a frequency is resonant it will make you want to turn down your speakers while listening at a louder level. This indicates an eq problem. Also, small loudspeakers are not able to reproduce some very low frequencies, so this may build up in the cabinet and make the audio sound muddy too.
After you have treated the audio with harbal and still have a problem try this tip:
http://www.har-bal.com/ipw-web/bulletin/bb/viewtopic.php?t=722Don't get too carried away with low-shelving though as it will take away a lot of the lower energy. His suggestion is to lower the lowest frequencies by 2db at most.
I don't know how you may feel about this, but you might not want to alter your original audio. Still, you can experiment with this to create a new CD which will sound better in your car.
Gordon