I think a lot of things can cause that. Unfortunately it's difficult to diagnose hardware issues for certain without just having a bunch of spare cpus, spare mobos, spare ram, etc lying around and a lot of time on your hands to keep swapping out parts until you find a swap that fixes it. Especially when it's an issue that happens occasionally so you have to keep using your computer without issue for long enough until you think it's likely that the problem is fixed.

Also not guaranteed to be a hardware issue but probably is. I've sometimes had similar issues that were a combination of the kernel not working well with a specific piece of hardware I use.