That's a nice NVR, btter than than the cheap far eastern ones.
You would need two RC snubbers, one between 13 and 14 and the other between 23 and 24.
The snubbers work by limiting the rate of voltage change across the contacts as they open. Fast rates of change = lots of interference.
Putting a capacitor across the supply does not stp the interference being generated, but stops it going down the mains cable. If it goes down the cable it can cause two forms of interference. The cable can act as an antenna ad radiate the interferebce or it can be conducted down the mains and into the stereo via it's mains input.
If you arre anywhere near Cambridge drop me a PM I may be able to help more.
Robert G8RPI.