How to get rid of hum from pc sound card?

You need to unplug everything, then plug back in one at a time to determine the source / cause of the hum. Then you'll be able to reconfigure your setup. Usually they run about 60 or 120hz. If the cause is a ground hum, then ground loop isolators can work very well to eliminate the hum.

1. Why do my PC speakers hum?

Why do my PC speakers hum?

What's Causing the Buzzing? One possibility is that the audio cable coming from the speakers isn't correctly plugged into the audio-out jack of your computer. The volume may be set too high, or the audio file you're playing back is corrupt. The sound card may be broken, or the driver software is corrupt.