I've just posted a similar thread specific to shimano A520 and A600 pedals. Try switching the pedals onto a bike you know is fine and seeing if the problem moves with them. If so, you know the problem is most likely the pedal.
You might be able to service the pedal bearings and solve the problem, not sure with this model though. This is how to do it with Shimano, though it doesn't show you how to strip, check and reset the dual cup and cone arrangement (your pedal may have different bearings anyway for all I know);
https://www.youtube.com/watch?v=KkH7gClG8NM