Going to say this is normal. Can you post a video?

If it does turn out to be an abnormal amount I would make sure that the flipper EOS switches aren't stuck closed. Are the flippers smoking hot after playing for a few minutes?

Only other things I can think of would be a failing Coil Bridge or Transformer. The coil bridge is on the wall in the backbox and not on a circuit board. It's just to the right of the 3 fuses and to the left of the lamp bridge. Easy to replace. Just a screw and 4 spade terminals.

Not sure that I've ever seen a bad transformer.

yep, normal.

Almost every pin every made can do this, some worse than others, and the older the pin the more it seems it does it. Have seen WPC machines do this. Haven't really noticed on newer Sterns.

not really, Controlled lamps normally do not pulse. How noticeable is the pulse? Usually 1 of 2 things is occurring when controlled lamps pulse.

#1 when they ALL pulse (not just most, but 100% all) then you have a bad lamp capacitor (the super large one) and/or a bad bridge

#2 when only some pulse (usually in groups of 8 ) there can be a miswired lamp somewhere. All controlled lamps should have a diode on the socket, sometimes the diodes are left off or wired to the socket incorrectly or a wire falls off a socket and gets wired up to the wrong lug on the socket.

Does Flash allow you to test each lamp by itself in diagnostics? If so run this test and make sure only 1 lamp lights at a time.

That pulsing is pretty minor, maybe add an extra cap to the large cap. When I have seen the large cap fail, the pulsing is much slower but has a much greater effect where they pulse about 1 second apart and the pulse is so great that the lights turn all the way off.

Pop bumpers lamps in Flash are controlled lamps (thus DC through the big cap)