We live in a terrace with lots of cats in the street. Several times in the last few months we have heard a cat meowing - in fact, I would describe it as yowling, over and over again, incessantly, sometimes all day. Each time we check outside, look around for our cat, but it definitely isn't a cat we can see...the point about the terrace is that the walls are very thin like a bricks width, and you can hear all doors closing, music, loudish talking , from both sides - so it could easily be in the house next to us.
The bloke there is a bit odd, very quiet, lives on his own, house is a mess on the outside, we have had a dispute for a while about his jungle garden and the sycamore tree in the front garden. Nothing against him as such, but the way he has left his house to fall into disrepair does annoy me somewhat, cause it looks bad, no other issues other than that. He comes and goes at odd times, so maybe works shifts or something, we barely talk to him really, seems ok but just a bit of a loner - has some cats, not sure how many. We know he comes and goes at odd times as we can hear him watching football in his bedroom, next to ours, at random times in the early hours or late at night. Also can hear him snoring...
So pretty sure the cat is his and it is coming from his house, or outside his house trying to get in.
So I am wondering - what if anything should I do? It is driving us a bit mad, I can hear the cat now, it is incessant meowing, as if it is trapped in or something. It upsets me a bit, if it were my cat meowing like that I would think it in pain or hungry, although ours does meow at odd times in the night, but she is a little bit mental and it is usually loneliness, cured by letting her sleep on our bed...
We hear it lots, for hours, then sometimes not at all for days, so I don't think it is trapped, as at times of course it hasn't been doing this - so I wonder if he is leaving to go to work or something at odd times and the cat is just not keen on being on it's own.
If I call the RSPCA to check up on the cat or other animals they will think I am a loon, surely?! I can't ask him, it would sound very odd, especially as we barely talk to him. He already thinks I am a cow as I don't want his ridiculously overgrown garden taking the slates off our roof with the trifid 'mile a minute' plant he refuses to do anything about 
Would anyone do nothing, or talk to him, or call RSPCA to check on the animal?