The Castlevania games typically have pretty good music for their respective consoles, but in the first NES game there is a way to temporarily turn it off if you have some bizarre reason to want to do so.
First, pop in your Castlevania cartridge and power on your NES. Then... don't touch anything. Eventually a demo will play
Let it go and cycle back to the title screen. Continue not touching anything and a second demo will play.
Let it go and cycle back to the title screen.
Finally, you can touch something!
Hit Start on Controller 1 and the game will start as normal, except when you get in, the music will be gone!
(It's real hard to get a screenshot of music not playing, so you'll just have to try it for yourself)
Once you do something that makes the music change, like fighting the stage Boss, the music will start up again and not go off, so enjoy it while you can!