Doesn't your music s/w have Ext recording feature? + How are you inputting the Guitar???
I don't think an ext card/box is needed - not to see if the PC will "record" anyway.
As BigB suggests, you need to change the 1/4 jack to 3.5mm, use an adaptor with care as the leverage is great. Better to use a short cable with correct connections (1x 3.5mm plug + 1x 1/4 skt).
Start with LINE i/p and find how to Record - easy in prog like Audacity(free download - DYOR) and playback via speakers/headphones/ext HiFi etc.
This will determine if there is any Buzz (your word)...I think what yr describing is mains pick-up ( room wiring), caused by long cables from Guitar - Worry about that later, but shorter leads will help.
The first thing to do is check the Levels are right to avoid distortion . . . only use "Mic-in" for low-level devices, like microphones! sounds obv but wth saying.
External Audio devices are somewhat better Quality than many PC's own soundcard - but the difference isn't much - rather as BigB suggested they have more rugged connections. Most will connect via USB, but only work with a PC.
Some folk prefer an independent recorder, using SDHC flash mem cards - like "Zoom" available Amazon abt £70 and these can record high quality via 3.5mm input skts [ hand-size, use AAA batteries-DYOR]. Good for gigs as their internal mics can record other sessions, eg for ideas, checking audience reaction, etc. I'd suggest one of these is a better 1st purchase for similar money. (and maybe stick with the _PC soundcard until you get tired of it.
There are some cheaper "video recorders" - similar audio i/p but with a small vcam so you can see who's playing - Vid quality is slightly poor, but audio should be OK.
With SDHC recorders you can playback (hedphones with good muffs for gig use!) or via hi-fi...or via PC where you can Edit the performance; eg in Audacity. - - - or a DAW prog.
Hope that helps.