We had this with the downstairs neighbours. Every morning at 4am give or take 10 minutes. Rather than say anything, we put together a scorecard on a bit of paper and called it Shagstar Superstars. Marks out of ten for Variety of noise, volume, artistic license, duration etc. I nipped downstairs, popped it under the door, knocked and pegged it. Upstairs we heard it all go quiet and then heard a new type of scream. Followed by a horrified 'OH MY GOD!!" It kept em quiet for a couple of weeks at least. Then again this depends whether your neighbours give a monkeys. Ours did but then got back on it after a couple of weeks. God knows why it was always at 4am. She yipped like a terrier. We were moving out anyway.......