It's been about 10 months (most of it spent travelling or in temporary housing) since I've been able to get my computer to record anything without all sorts of noise and interference. I finally gave up on trying to find the source of the problem and just started to overhaul my computer, starting with strip a bunch of bloat ware. Eureka! It works again. Here's test recording #1. (I still have no monitors so I'm kind of guessing at the sound but at least there are no pops or obvious hiss that I can hear.