I have a highly strung cat, he gets cross if he can see other cats walking down the road for example, full on fluffy tail growling type reaction. Especially to one cat he is having a feud with.
Since moving he has sprayed in the house, not every day.
Tray is clean.
He knows where his tray is.
He is fine in himself.
Diet is wet and dry plus I see him using his water bowl.
I'm wondering if it could be idiopathic cystitis caused by the stress of living in an area with a high density of cats or if he's just scent marking so that if one of the other cats happens to be in our bedroom he knows its our cats house?.
I want to get a second tray upstairs but dh is resistant to the idea 
We are going to book him in at the vets for Tuesday.