My 14ish year old male cat, Tarzan, has been doing that all his life, but only a couple times a week. He start walking around the house doing that loud merrrooow, merrrooow thing for a couple of minutes. When I use to go see what was up, he'd turn and look at me like "What?!?" I use to think maybe he was calling for our other cat, Agatha, but she can be in the same room with him and he still does it.
Cats - who the heck knows what's going on in their heads!