Greetings Draege,
It's quite common to get vibrations without noise! Not only does it vary between people, but it varies between your own experiences! The first time I got vibrations, it was accompanied by a humming, but ever since then, I just feel the vibes.
The sounds that are often discussed aren't always about vibes. When in a deep trance and when your etheric body expands, you become susceptible to auditory noise.. doors being slammed, whips cracking, voices, etc. These are indications of deep trance and eminent projection.
Also, keep in mind, not everybody gets vibes either. [;)]
I've been practicing (trying to) OBE for a few weeks now, and believe to have gotten vibrations about 4-5 times. However I read on this board that vibrations are accompanied by loud noises though I've never experienced that. Is it possible to have vibrations without the noise?