Why are you direct connecting a computer to the modem? 

If you get even a cheap router you can connect multiple devices to it and use the wifi. 

Plus it gives you some firewall protection versus when using a direct connection, there’s nothing. 

I am intentionally not using wifi, one of my pet peeves! I always hardwire my laptop. So I identified the noise is coming from the power supply not the cable modem. I purchased a refurbished laptop and they must have sent a faulty power adapter. What a waste of time.

Fair enough that you found it wasn’t the modem. 

I’d still advise picking up a cheap router and disabling the wifi. That way you at least have a firewall for a little security. Otherwise  it basically leaves the computers connected to the modem wide open for someone to access. Antivirus isn’t enough if you’re running it direct connected. 

Plus many routers have a hardware button (not all) that allows you to turn wifi on/off. That way you can turn it on when you need it and disabling it easily.