My original iPhone 6+ had a very quiet vibrate compared to my replacement unit I got months ago due to a wifi issue I had.
Anyway, I got sick of the vibrate being so loud so I decided to open up my phone and take the 3 screws out that hold in the vibrate motor and then simply reinstall them tightly. It has greatly helped with the volume of the vibration on my phone. Sometimes I don't even realize it vibrated when it's in my pocket where as before I could hear it vibrate in the next room over.
Anyway, I got sick of the vibrate being so loud so I decided to open up my phone and take the 3 screws out that hold in the vibrate motor and then simply reinstall them tightly. It has greatly helped with the volume of the vibration on my phone. Sometimes I don't even realize it vibrated when it's in my pocket where as before I could hear it vibrate in the next room over.