Hey Scott,
Compressors are an evil entity. They can best be described as "temperamental". Of course after your session with the loud "hissssss" you may pick another word
The hiss is NOT a malfunction - it is simply the compresson "bringing UP" the noise floor. It doesn't know the difference between a good noise and a bad noise. The art lies in sending the proper signal to the unit and using the compressor to "wisely" adjust the peak levels. This is a science all it's own. A few general rules apply -
1) Less is more - don't overdo it or the sound will loose it's dynamic quality and sound squashed instead of fluid
2) Try limiting instead of compression - most often the offensive levels just need a little "rounding off" to present a smoother, more consistant product.
3) Don't use a compressor IN PLACE of proper mic technique - the same "garbage in - garbage out" advice aplies to vocals too!
4) Specifically - your voice doesn't seem to need too much processing - it's smooth and even. What end result are you after?
5) Try a ratio of 2:1 or 4:1 to start with. If that unit has a gate - set it so the gate shuts during silent passages and opes at your lowest breath - it's really clean up the track. If you do compress vocals directly, make sure you don't squash out all the dynamics - just work on the extreem ends; top & bottom. Good luck!