Audio is on a shared IRQ (Interrupt) with a higher priority device. Thus the higher priority device can interrupt the sound if it needs to do something and thus you can get the stuttering. There can be other reasons but this is one to consider.
Uninstalling the sound, restarting the PC and then when Windows starts it will detect and reinstall the sound and sometimes Windows will install it on a different IRQ and help with this problem.
Go to the Device Manager, RIGHT click on the entry for the sound and then LEFT click "uninstall". DO NOT check the box to also uninstall the drivers. Restart the PC.