Just got a Lumia 640 to try out, nice bright orange color with good quality expected from Lumia phone, with exceptional price, definitely value for money.
However, as the phone does not have any soft button, the navigation bar (Start, back and search) is directly inside the screen. It is quite irritating that the phone always vibrate upon pressing any button in navigation bar. I did a bit of research, and it's actually quite easy to turn it off:
1. Go to Settings, search Touch.
2. Switch off the Navigation Bar. Initially, I thought this was meant to switch off the whole Navigation Bar, but there is text below "Vibrate when using Navigation Key".