[LAU] General Audio question - soft recording and bad SNR?

Hi, I'm running Arch Linux 64-bit with jack2. I have a USB UA-25EX to which I connect a Shure SM75. I don't do much recording, and at a very amateur level for various volunteer projects. The maximum volume I get from my Shure SM75 seems very low. The result of this is when I normalize I get fairly significant background hum. Increasing the UA-25EX's gain just causes peaking at louder volumes, so no solution there. This happens with both Audacity and Ardour, so should not be software-related. Any suggestions as to what I should investigate? A bad mic (I did check, its not a knock-off)? Electrical noise from my laptop (used to use a different laptop but from the same manufacturer, same results from both). Jack settings?