I think it is hardware. I got the new phone and rediscovered what it was like when I got the 1st one, almost a year ago. I forgot that the windows button is supposed to vibrate softly, and phone calls noticably. So, the vibrator motor had been failing and finally just broke. It was pure coincidence that it failed around the GDR2 flash. I see the complaint about the extreme loudness of the vibration in several posts on this forum. Then some say it has gotten better. Does "better" mean that it is failing? That's not better. That's broken!
One of the tear-down websites stated that the 920 build was really out of Nokia's expertise, one reason it is so heavy, a cobbling together of disparate parts with a lot of glue. The front camera on my phone was full of dust within 8 months, which was one manufacturing defect. Perhaps there is a glue failure on the vibrator motor? I know Nokia is a lot better at the luxury smartphone now, but I suspect I will begin to see the same problems on this 920 in about 6 months. I will be seeking a WP replacement before that happens.