This was happening to my '14 silverado. Took it to the shop. Turns out my brake fluid was low and brake line was leaking. Had to get it repaired. I'd start there. Other things that were happening due to this included my stabilitrak and traction control turning off/on.
This started happening to me a few weeks ago. After some research I found my brake fluid to be low. Took it to the shop, truck needed new rotors, new pads, and new brake fluid. Since then, the e brake light has been off. I'd take it to the shop for a brake / brake line inspection and see if they come up with anything.