My audio has a loud spitting, background noise

when I'm listening to Internet sources directly.

But no background noise when listening to videos downloaded from YouTube or audio downloaded from the Internet.

Any suggestions re sages ?

Noise is like what they used to call "hash" in amateur radio

Sounds like this

https://www.youtube.com/watch?v=wffIdh0CZWs

but the volume rises and falls a lot

Weird.  That's an analogue interference sound so it's either on the source audio or it's local to your PC.  On-board sound or discrete sound card?

I don't see how it could be source or sound card related since there is no noise when I download the file (using Total Recorder) and then play same

Are you using wired speakers? You might check the wiring connections.  I had an external speaker that had this problem and turns out it was a volume control with a bad connection.

Surely if the problem is wiring or volume control related, the downloaded video and audio would be noisy too.

I will add that when I said the noise was loud, I should have said it is mildly noisy, enough to be very disturbing.

It's a strange one.  Not something I've come across before.