When I am plugged into mains two of the six lights in my van flicker.They don't do it simultaneously and it's just two of the rows in each bulb-the other rows stay lit as they should.The only other power being used is the fridge but this can happen when it's not on.
When I tried to demonstrate prob to my dealer of course they didn't flash.
When I tried to demonstrate prob to my dealer of course they didn't flash.