Why does my finger buzz when I slowly move it near the trackpad? I've noticed that when I drag my finger around the trackpad (not actually on the trackpad) that I get a strange little vibration. Is the haptic engine responsible for this? and why does it do it?
Normally this vibration sensation is due to the MacBook being plugged in. From personal experience my 2008 MacBook Pro does this when plugged in (Official Charger) and my 2012 MacBook Pro only does this when plugged into the college power (Official Charger) so cant say for sure as I don't have your specific MacBook but am confident this may be the answer.

As you stated with the haptic feed back this could be the answer as there could be a software bug causing the vibration to be stuck on but I can't help thinking this may not be the case.