It is a loose connector inside the phone. I have had the issue with other phones an old E815 comes to mind, but never did with the Dinc
You might try calling HTC an see if they can fix the issue or if they could send you a replacement D.inc. mine has'nt went over that Hurdle yet but with it being over a year old as well it's kind of raising those back Hairs B33....I found my Colors Yeaaa!
An to All Please have a Safe! an Happy New Year!