Aaww, you got two kitties, God bless ya, one new one is killing me. If the kitty is 3 plus months, it might be marking territory and I would get him to the vet to be fixed. My Smokey was fixed at like 4 1/2 months because he already started spraying. He did it behind the TV in a corner. Where ever they pee, put a bowl of food over it and they won't pee there anymore. It worked for Smokey after a couple of times. Plus there are sprays out there you can spray to deter them, but I'm not sure if they work.
My best guess is he is going into heat early and is marking.
Anybody else got anything?