Cactus Music
Have you worked your way backwards, 
Disconnect everything
speakers on -listen
connect speakers to Zoom- volume down --listen --volume up ---listen
Connect Zoom to PC - listen and on and on... 
 
 
Weird sounds can come from unexpected places so the only way to trouble shoot is slowly adding or subtracting until it goes away. 
I had a crackle in my left monitor when playing bass heavy music, I thought the worst, turned out was the AC cord to my sub woofer was loose and somehow sending the crackle to the monitors. Why only the left was the mystery.   

I read about a USB Ferrite cable that may help block computer noise.  I will also take all these good suggestions and tear down to PC and Zoom and start adding thing back.  I will report back soon.
 
Thanks to all.
 
Rimshot

gustabo

Rimshot

gustabo
Are you using balanced or unbalanced cables to connect your speakers to your audio interface?
 

Unbalanced.

Is it possible to try balanced and see if that gets rid of it?
 

My Nano Patch does not have balanced out to the speakers only balanced in.

Update: I installed a new USB Ferrite cable between computer and the Zoom R24 and it did reduce the high end noise but did not eliminate it completely.  I can live with it now. 
 
Thanks for all input.
 
Rimshot
 

Do the powered speakers (what brand and model are they) have balanced inputs. There is a way of wiring from unbalanced out (nano Patch) to balanced in that sometimes eliminates noise. It requires you to make a special lead. It might work in your case but you need a proper balanced input for this to work.
 
For example when I connect a stereo mini jack out (IMac) or most computers to two line inputs on my digital mixer (even though my line inputs are balanced) using the normal approach of unbalancing one side of the balanced input, I sometimes get high freq noise like you are describing.
 
I have made a special lead now that connects to the balanced line inputs (not using the normal sleeve earth that is) and this noise is not present when I do it this way. It may work in your case too.
 
 

Rimshot
Update: I installed a new USB Ferrite cable between computer and the Zoom R24 and it did reduce the high end noise but did not eliminate it completely.  I can live with it now. 
 

If this helped you may want to consider adding a few more 'clip-on' chokes (ferrite beads) around the USB cable.  Just the one on the cable might not be enough.
 
Glen