Always when you are at someone else's house you have to get used to a lot of new sounds.
In my parent's house, not only does the microwave beep when it's done, but so does the dishwasher! The fridge and the freezer hums loudly and my Dad's computer is set to a very annoying (and loud!) sound that echoes through the house when he receives an email. His other computer has a screensaver, with a clock that strikes (loudly!) every now and then, but never regularly; and Mum uses the "seal" notification for her emails...
Add to that the normal beeps and blips and notifications on our different phones and iPads, and no wonder sometimes it gets a bit much.
The other day there was a loud beep, which none of us really recognized. We looked at each other when we heard it and puzzled asked each other "Is that yours?", but noone wanted to acknowledge it.
My Mum went to investigate, luckily, because outside on the yard was the postman (in his car, they live in the countryside), it was him that had honked the car horn because he had a parcel to deliver!