I’m in a thin-walled modern semi and my next door neighbour has what I’m pretty sure is an airlock in their upstairs toilet/plumbing as every so often (presumably when they flush the loo) I can hear what sounds like a loud low rumble like someone playing the tuba for several seconds, then it eventually tails off into silence.
It’s driving me mad, it wakes me up first thing in the morning and often last thing at night and makes me jump several times during the day. I was in my front garden earlier and could heard it then too so it is LOUD.
My next door neighbour probably doesn't realise the sound is travelling through the wall. I’ve not really spoken to them much as we never really pass each other out the front - is it still acceptable to knock on the door and to mention it and ask them to raise it with their LL? How do I word it so I don’t come across as a whinge bag who will only knock when there’s an issue?