hi Phil,
I've had this problem for over a year,I've tried all sorts of lubricant,the last being a ceramic spray for bicycles from wilko £2.50 it will quiet it for quite a while but it will come back,Eric the car guy on 'you tube' said if you put the cotter pin back the other way round which will make it easier to do another time,I am going to do this when the weather
is better and coat the cotter pin with lithium grease at the same time as i think the cotter pin is the cause where it pivots,i think there is slight wear,i have a small piece of bamboo
to push the cotter pin out with to keep the pedal in place.hope this helps,you need to remove the panel by the pedal for access.