Presonus Audiobox and the Scarlett 2i2 like KonKossKang said. Even those will make a difference and give you better results...speaking from my experience. While in some case you can get by without a audio interface depending how in depth and detailed you get with your music. Later on as you get a better ear or switch locations you may notice hums, computer fan, hdd, pops when other electronics are turned on or off. Also you may have a pair of monitors that you don't have the connections for or your cables are introducing bad signals to your recordings. Having a audio interface will leave you with a way to expand or at least have more options to standard pro audio connections and gear. I used to ask the same thing and believe that asio4all would do it, but as I grew I learned how much I was limiting myself and making it harder to achieve better quality using crappy RCA cables, 3.5mm jacks unshielded cables at that. While asio4all can give you better latency than the stock drivers it still wont fix everything in the sound.
The onboard jack usually does sound way different from the interface to me from USB or firewire interfaces. If I listen via my onboard 3.5 jack everything sounds overly enhanced, closed, smeared, compressed bottom end, and loud. Along with with the sounds of the hdd loading and ground loop humming. I tried on various computers and interfaces. Not saying a audio interface will fix all your noise interference...but usually you wont have any especially with decent cables and making sure you taken care of grounding issues if any. Keep this in mind Beats audio, Realtek, SRS, etc are not made for pro audio and are more for listening and doing average user tasks for multimedia.