I've noticed it a few times now. When I first turn on the hallway light it has some minor flickering for 2-4 seconds and then stops. If I turn the light off and back on it does not do it it seems to only be when I turn it on from a cold start. Recently a lot of more lights were added to this circuit but they were not on at the time of this but could that still have something to do with it?
* The first time I saw it I changed out the light bulb but that didn't help.
The switch could be wearing out, including for such reasons as old age.
A typical light switch will handle several light bulbs.
When installing a new switch, wrap the wires around the screw terminals to attach them. Don't use the push in holes in back unless a screw is provided and absolutely needed to hold the wires in place back there.
When cleaning anything including baby diapers, it is better to sweep off or scrape off as much solid and semisolid material as you can first. (1) Less cleaning fluid or detergent needs to be used, (2) Less of a mushy mess which in turn means that bleaches or disinfectants will be more effective.
Is it a fluorescent light or incandescent? If it's a fluorescent theres little you can do. (In some instances "older models" a starter will be present in the fixture. You could try replacing that). Replacing the fixture is the only other option.
If it's an incandescent, tighten or replace the bulb.