Help! The Sound On My Laptop Has Gone Weird & Even A Reset Hasnt Fixed It!

[joko]

the speakers on my dell precision M6800, running Win 10, have gone all crackly and buzzy whenever a sound is being played - and sometimes, when, there is no sound playing it will just start playing different buzzing notes, continuouly, changing through a few notes every second.
when it happened the computer became almost unusable - serious lagging, fluttering, unresponsive etc
its happened before, a while ago, but running trouble shooter, altering settings, updating/changing the drivers & updating windows etc usually fixes it.
I uninstalled the drivers & the device & nothing changed.
a few system restores failed - they just carried for hours & i had to restart with the button.
so eventually i did a system reset - which isnt back to factory settings, but it removes all programs & settings, & reinstalls windows, but saves my personal files.
it did keep my colour theme & background though so it saved some things.
anyone any ideas of what else i can try? please help!
Im assuming the next step is going to be full factory reset, if i cant find a solution.
Its RealTek Audio
thanks :)