I've been scouring Google and trying to read up on this. Similar experiences seem to be caused by a bad ground wire (usually associated with either the power outlet or surge protector it is attached to). My problem persist even when not plugged into anything. So I've read it may be due to some bad ground soldering inside the laptop itself? To test this, whether or not the problem is isolated to the 3.5mm jack itself, I went and plugged in to every audio device I could get my hands on and sure enough I can hear the same fuzzy sound with just about everything (it is just WAY easier to hear while using headphones, which is what I use most often).
So I don't know if that means the jack itself is bad or if this is inherent in all Servals? Maybe the jack is just too close to components inside the case and there is interference? I'll wait for you to test some tings out on the Serval obviously, but worse case scenario do you think something like a USB to 3.5mm is plausible? http://www.vpi.us/usb-audio.html