If it happened when he changed his video card, I'd be suspicious of when the audio source changed at the same time (like he's now using HDMI audio), since changes in audio renderer can cause issues with jerky audio.
Hey guys, I updated all the drivers on my Windows HTPC as well as tweaking a few settings in the PVR client settings in Kodi (set refresh rate to 59.xxHz for instance)
Not sure which step fixed it, but for now it is playing back smoothly again.
Thanks for prompt and helpful replies!
Cheers,
_Fonz