The low hum seems normal. A soft pot always reads the lowest value, until you press somewhere higher, and as soon as you let go... bam it goes back to the lowest value. You use that feature as a gate, as soon as you press somewhere, your voltage is bigger than a certain value, so using a simple ">c" object, you can then send out a gate signal. I have an extra ribbon for pressure underneath for more expression (but that's something else)
here is a small easy patch that should work. You may need to filter out the signal before the gate, to get rid of the noise sometimes, but that's usual with GPIO's anyway.
Voila, hope you're enjoying the softpot, it's great when you start having fun with it