@Inna22 was this the one who sent the "make sure the place is clean and the oven works" message? Ay yi yi.
I would just say "Sorry you have been disturbed by noises. As I offered, I am happy to have the police stop by if you think this is beyond the natural ambient sounds of an urban location with shared walls. I have not had any other guests report a break and enter, and will to have this checked thoroughly for my home owner's insurance, so please let me know when you would be able to meet with the police."
Put the impetus back on them. This is your property so if someone really was to mess with it, you would need to investigate. If its too inconvenient for that to happen, then obviously they can't feel that darn unsafe.