I just repaired this kind of left-sided click on my bike. The left pedal outer bearing was dead even if not that old. There was no sand inside or anything like that, but the bearing is really grinding even in my fingers and the click is gone with a new piece.
Of course, your case might be different.
A lot of carbon-fiber frames with press-fit bottom brackets have a problem with bottom-bracket creak. This is because press-fit bearings depend on the bearing cups being perfectly parallel and in line, and the frames are fabricated with the bearing cups out of spec.
There are replacement bottom brackets that come with their own sleeves that thread together ...