Cat becoming scared and aggressive

Our cat has recently been going into our laundry room and becoming very scared and aggressive. He'll sniff around for a couple of seconds and then start meowing, hissing, and spatting at anyone that comes near him. He meows like he is frightened by something. He first did this last night when my uncle was washing his clothes. We thought he might have smelled something that frightened him on my uncle, but then he started sniffing and tried to get behind the dryer. He did the same thing again this morning while my dad was in there, and again earlier tonight while I was in there. He only does this in the laundry room. Does anybody have an idea as to what is causing him to behave this way? I'm pretty sure it isn't a mouse or anything, because he's seen mice before and doesn't act this way when he does. Please help! Thanks

My cats act like this when they see another cat outside. Are there any windows in the laundry room? Any chance another cat (or wild animal) got behind the dryer and sprayed there? I think even a mouse might scare them if they only smelled it.