Have a friend whose MacBook was having this same problem. It was driving him, AND ME wild. I told him, FINALLY, to call Apple. I was stumped.
Guess what solved it. When he put his MB back in his BIG laptop bag, he had to rearrange the stuff in the bag, which included a WIRELESS KEYBOARD.
He had forgotten to turn it off and something was pressing against the keyboard, so the key sequence kept on repeating. It was a number 3 if I remember correctly.
I sincerely hope that this happens to be your problem.