I don't have enough information so I'm just going to assume things. One of the possibility is that the sound card driver that is automatically provided by Redhat to your soundcard might not be the best one. It works, but that's probably the disadvantage you get from it.
Another possibility, is of course the sound settings. If you're using Red Hat or Fedora with GNOME, you should be able to see a volume icon bar on the top right hand corner. Increase the Master and PCM as necessary. Be careful with increasing PCM too much as it tends to make the sound to bassy as well. Normally I have it as almost full but not completely.
I hope that helps a bit.