Audio Playing Through Two Comps

I just moved in with my friend a few days ago and after we got our computers set up, my friend put on some music. Instead of it coming through his speakers, though, it was coming through the T.V. I use as a comp monitor, and once he got his speakers working it was playing through both my T.V. and his speakers.

At first I thought it was because my smart T.V. was hooked up to the internet, and it's not, so I have no clue how to make it stop. Aaaany help would be much appreciated.
 
First, disable BOTH to prove that's how the access is being done.
Then, reenable one and see if it repeats and finally add the other to recreate the proble.
 
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