We live in a terraced house. The walls are thick so there's usually no noise from either side, but one of our neighbours - who lives alone apart from his cat - regularly shouts FUCK OFF and growls SO loudly and angrily that it's genuinely scary! The anger in it makes your blood run cold and once I thought he might have been being attacked or something. I can't work out any explanation for it at all. It usually happens first thing in the morning, but can happen any time of day, most days.
It's not bothering us that much, except when it wakes up up at the weekend. It's just weird and makes me quite wary of him. He's not friendly - if we pass he'll grunt hello but hasn't ever seemed to want to chat, and I don't try now. He looks completely healthy and 'normal' and drives a vv expensive car so I assume he's got a good job. Any ideas what could be causing such violent anger on a regular basis and would you say anything?