Unplug the speakers from the PC and see if you still get the buzz with headphones. Some "buzz" problems can be related to "AC power ground loop" problems if some separately powered devices are connected.
Noise and skipping are problems that have been posted here before. There is no "one fix" for that. There are possible hardware problems, drivers (including video drivers), Interrupt issues, Wi Fi caused, etc.
Skipping can be because the other device that is on the shared Interrupt that the sound is on is interrupting the sound. Sound is always on a shared interrupt (IRQ) with a higher priority device. You can try this: go to the Device Manager, RIGHT click on the entry for the IDT and then LEFT click "Uninstall". DO NOT check the box to uninstall the drivers. Then restart the PC and when Windows starts it will detect the sound and reinstall it and some times put it on a different shared IRQ.