Here's a good clue that the PC can't keep up or something is amiss causing the PC to hang/freeze while it services whatever and bogs it all down. The audio/video side because they are real time events that an user can see offers that a problem is present. You have to look at what's installed as in pgms. and if all was well until a recent install, look there. If any recent video/audio updates, look there. If the PC was working well before any of these problems arose, then again if something new was added or updated, look at those recent actions.
If you had Win7-32 bit running and now the -64-bit version, then make 100% sure you have installed the 64-bit versions of any updates and/or drivers. If this 64-bit was installed over the 32-bit version, now you know why its best to install fresh, now as an upgrade over existing install.
Ruled out, "electrical interference" hardly, sometimes that comes by way of the PC slot its installed in. Try another, to help reduce that as a cause because noise generated by the PC itself can't cope because overall its a simple level of suppression.
Your details are fuzzy, be specific, new or upgrade OS install?