I have a SRAM Force crank with Look KeoMax2 pedals with ~1800 miles. There are three spacer washers between the crank & pedal, to get my fit correct (drive side only). I use SIDI Genius 5 shoes.
Recently, there has been a tick with the down-stroke on the drive side, especially when climbing. I took the pedal off, reinstalled it & tightened it down good. Still the tick. I then put the pedal from my wife's bike (same pedal, less miles) on mine, and I have the same problem. I took her's off, cleaned, lubed & installed mine back on the bike. Same problem. I also tightened my cleats.
If I remember correctly, there was a very loud pop that came from somewhere on my bike around the time that the ticking started. I have a carbon frame, with no signs of cracks or damage. I have not crashed this bike.
Everything seems tight, there is not any play in the pedals, crank or BB.

Does anyone know what this could be?