I'm not sure about your boyfriend hearing something as that sounds semi 'off'. Just being honest. Let's deal with what YOU feel.
You did the right thing to go to your ob/gyn and have an evaluation. I hope that you told them about the sensation you've been experiencing.
If that reveals nothing, still continue to work with your doctor. The genital area is quite vascular and contains many nerves. Believe it or not, a pulsating, tingling, vibrating feeling in the vaginal area is common. Unless it is painful, it is typically no reason for concern. https://www.medicalnewstoday.com/articles/vibrating-vagina
Something that could be helpful is to try pelvic floor exercises. My Y has a yoga class for this but you can certainly find so many on youtube or whatnot. Pelvic floor dysfunction is when you have weak or tight pelvic floor muscles. This can happen for different reasons.
Also, you can have muscle spasms brought on by stress, anxiety, fatigue or nutritional deficiencies.
Also, read about Vaginismus. Another fairly common issue. https://www.webmd.com/women/vaginismus-causes-symptoms-treatments. That does take you back to what is mentioned already. Doing things like kegal exercises or looking into the stress/anxiety issues.
Probably the last thing I'd consider is a nerve entrapment. It can happen. Stretching can relieve that.
To add additional information on the noise my boyfriend hears, he says it sounds like I have a vibrator going in my vagina/anal area.
To his credit he is able to hear it and tell whenever this is happening to me even if he’s in a different room/area of the house (that’s how loud the sound is).