Powering a car audio amp with a PSU: Interference when laptop is charging but when unplugged interference is gone?

Hi, I hooked up 2 car speakers and a sub to a car amp using a PSU. There's a constant interference emitting from the speakers when the laptop (which I'm using as a source for music) is plugged in and charging as well as the PSU. This stops when I unplug the laptop.
Any suggestions about what can be done?
This is the original instructable that I was looking at. Unfortunately the maker couldn't solve my problem. https://www.instructables.com/id/Car-stereo-PC-power-supply-with-pizzazz/
Any help would be appreciated, thanks!

Are they plugged into the same outlet or two different outlets?

Sounds like a ground loop when you got two different pieces of audio equipment with different grounds.
Try plugging them both into the same outlet, make sure the PSU is properly grounded.
benmurton4 years ago
when you have the laptop plugged in do you have the laptop charging? This maybe caused by bad earthing or other electrical problem and AC power running through the audio jack and being picked up from the amp. I have also heard of something called a ground loop which can cause some interference when you have two earthing points. if you can you my want to try a two prong adapter on either your laptop or PSU and see if that works.