First, make sure you are using the HP provided sound driver
and not the generic Windows installed "HD Audio Codec". In most cases the vendor, (in this case HP) provided sound driver is needed for proper operation.
Second, does this happen if the Windows Media Player is the only program you have open?
Finally, because Audio is considered a low priority item in Windows it is on a shared IRQ (Interrupt) with some higher priority device, that can cause sound interruptions. Uninstalling the sound in the Device Manager (but not the driver) and then restarting the PC will sometimes put the sound on a different shared IRQ and help to minimize interruptions.