super-famicom
Member
Soundblaster Z here. Did it because onboard sound was not doing it for me, and the promise of any kind of performance improvement (no matter how slight) is very tantalizing to me. Pleased with my purchase. It's particularly great for my headphones, as the onboard sound had a very hard time outputting enough power for a decent volume.
Try reseating it, make sure there's no wires touching the card, etc.
I had this problem too, until one day it magically went away. The card itself is shielded, so physical contact/seating problems are the most likely culprits.
If you need to increase the volume to very high levels to get your headphones loud enough, you may need an amp.