LT
You may have a bulb burnt out.

boogie_4wheel
A fast flash rate indicates a burned out bulb (or one that isn't working). Since it is an intermittent issue, I say that you may have a loose bulb in the socket, or faulty wiring in the circuit for that side of the turn signal system. Try to recreate the problem. Select the side (left or right) turn signals that you were having the problem with, then remove the front and rear bulb sockets, and wiggle the bulb and wiring to try to make it happen again. Also try to find out which bulb is not working the next time it happens (exit vehicle and do a walk-around inspection to see which isn't flashing). I once had the socket go bad on the front of my truck. No reason, just the bulb no longer made good contact with the contacts inside the socket. Replaced the socket and works great.

Juan V
You need a new bulb dude.

haskivenu JPAA
Have you checked the fuse is okay?