Are the sketches and work planes on at the part level? If so, turn them off there. If they are on at the part level they will show up in the Assembly level. A lot of people will get lazy and use the View Tab > Visibility Panel > Object Visibility drop down to turn off all the planes and sketches at the assembly level instead of making sure all items are off at the part level. This works fine until you need to see just one or two planes for some reason. I know there are probably some ilogic rules out there that can dive down to all parts and cycle the visibility of planes and sketches off.
Hope that helps.
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