Hey Mark,
       The following web page has instructions on how to use capacitors to
cut out the really low notes that your speakers can't handle.

http://www.matey-matey.com/capacitor_crossovers.shtml

It's a foreign page for Golf owners, but a stereo is a stereo.  If your
speakers are whomping or blapping on the lows, this trick erases it and let's
you listen to cleaner louder music.  Also, make sure the speaker isn't torn
or damaged. and is well seated in it's mounting.  If it is loose or can flop
around, you have to fix that first.
Good luck!

Bill Marshall
85 GL Tiico "Pandora's Box"
Bradenton FL