EDIT: Resolved Problem
This issue was caused by Widget Calculator + Log from VETAL (when enabling vibration on widget)
Have you resolved this issue?
I'm personally on T-Mobile but have been doing a ton of googling/reading on this.
I don't know if we're having the same problem, but here's mine...
Phone recently started vibrating at random. Vibrations are quick 1/2 second bursts every minute or so.
This happens regardless of the phone being used or asleep (locked). T-Mobile had me reset to factory settings (wiping phone).
Still continues to vibrate, though now a bit more sporadically. This has NOT occurred in the other two GS4's my family has.
After doing a bunch of research, turning off all "Smart" features, clearing cache from Recovery Mode boot, etc. - still no luck.
It seems MY particular problem is Android-wide, regardless of device or provider (though seems very prevalent in Galaxy line).
Some speculation is that this is resulting from a background force-close of misbehaving app or creation of a bug report - all behind the scenes & inaccessible w/o root.
Tomorrow I should be exchanging my phone at T-Mobile in hopes that it is hardware-based and simply a defective device. (Wish me luck)