On-board audio is often suspect to interference from the system itself. Many components in a typical computer produce some level of RFI (radio frequency interference) and on-board sound is great (not in a good way) of translating that interference into noise/static.
You really have 2 options. Get a discrete sound card (for desktop systems -or - notebooks can add a separate USB sound device as an alternative) or live with the limitations of your particular sound config.
Streaming audio/video, where the stream carries higher quality data often bring these deficiencies to light as the system has to work harder to decode the feature rich data stream. I would imagine that under normal conditions, your system performs just fine.