I'm vibrating them silently during the night too, if my parents would find out, they would kill me lol. Stay safe, do it when you are sure you won't be disturbed
yeah, use a fan and even a bit of music if need be to be slighty louder than your voice to make sure the sound is masked. there also a thing you can use over your mouth called the "beltbox" that muffles/lowers the sound of your voice, its meant for voice/singing practice, while a full out vibration would still be heard, if you are on the quieter side then it should help minimize the vibrations that carry through the walls.
Actually you can vibrate "mentally" too, but this type of meditation is weaker, than vibrating loudly. Use mantras, runes when it is the best to you or use music during meditation. But you can actually use yogic breathing technics too for your evolution.