I'm pretty sure my bad nights sleep was kicked off by hearing my neighbours having a massive barney so during my many awake hours I was thinking about this.
If your neighbours were having a huge row and you could hear things being thrown/banged around, when would you feel (if at all) like you should get involved? Maybe call the police?
After it had gone quiet I kept thinking what if she's hit him over the head with a saucepan A La Pauline Fowler!
I have called the police in the past on about three occasions (none of them were same people) but there wasn't really any lack of certainty about what was occurring. I wouldn't knock on the door myself and I wouldn't offer a hand in friendship particularly I don't think.
My neighbour is continually arguing with his new(ish) partner - She seems to be the one screaming and shouting but I think he's the one who's getting the raw deal. He throws her out, next day she's back and it starts all over again.
As there are no children involved and there doesn't seem to be any physical violence going on I guess there's not that much that can be done.