I notice that when I listen to Mel Tillus
Sorry, I couldn't resist.
Actually, I had the stuttering you are experiencing when I had my old sytem configuration. 600 Mhz 128 MB Ram when playing streaming audio or video. When I upgraded to a 1.8 gig 256 MB DDR Ram, I never noticed it again. I'm not saying it definately isn't Outpost, just my experience. You can check it simple enough. Just temporarily shut outpost while listenening to the music and see if it makes a difference. (obviously don't have any browser or email windows open at the time)
Let us know what happens.
OS: Windows 7 64 bit Outpost Firewall Pro ver. 9.3 (4934.708.2079)
Firefox 51.0.1 Thunderbird 45.7.0
SuperAntispyware, MS Security Essentials, AdWare Cleaner, JRT