I just moved into a new apartment and found the noise at night. It sounds like a big exchust fan running 24 hours. It is not loud but I can hear it clearly at night. I have some difficulty in sleeping now. The agent didn't tell me this when I rented the apartment. I really feel bad as I think they should tell me this. It is difficult to hear it at day time and I cannot find it by just coming to have a look. How can I protect myself?

You can do the sound level measurements, but if it's a fan or part of a building installation then I'm pretty sure that the sound level is within the legal bounds.

Sorry to say that, but renting a good apartment is a rocky road. There's plenty of gotcha's to watch out for. Look at the forum - at least you don't have toddlers above, neighbours working on night shifts, people with certain affinity towards noise and parties, etc. You could have done some basic reconnaissance before renting the place - asked the neighbours (there might be people for whom the noise is acceptable but who are aware of it). If the noise is within the legal bounds then it would be good to find out what is the source of the noise and then. It might just need some fine-tuning or maintenance - talk with consierge, etc.

PS. If it's monotonous humming then ear-plugs should be perfect. Some would like such sound as it tends to mask other more artificial ones. However this is a very individual issue...

Check the toilet and bathroom (if they are separate). Some newer apartment buildings have a separate switch for the fan. I know that I have trouble sleeping if somebody leaves the one in the toilet room on.

Maybe it will not make you feel any better, but something much worse happened to us. We moved to a big, bright flat only to find out a few days later that really disgusting smells of cooking and sewage came through open windows several times per day. At first we thought that it was an accident, then we realised that it was a regular feature of the building.

It turned out that there are ventilation pipes exiting on the roof and we are on the top floor -- amazignly, other neighbours do not have that problem because for some reason the stinking discharge lingers on the roof.

We should have done a better research -- there is a restaurant on the ground floor, so now at least we know that we would never rent a flat where there is a restaurant near.

We complained to the property management company several times. Other neighbours from the top floor did the same. The owner annulled the lease agreement with the restaurant, the restaurant appealed to the tribunal, I was summonned as a witness -- two years later the restaurant is still there but the situation improved -- I guess the owner was required to make some modifications in the ventilation and sewage system.

Check with the concierge if the noise remains and can not be switched off -- perhaps it is not normal and maybe the owner can do something about it.

It could also be something to do with the heating system. We had a new boiler installed in our apartment building in 2006 and when the Winter came and the heating was running at full power we found there was a whirring noise which wasn't really that noticable during the day when there is other noise but was like a mild rumbling noise during the quiet of the night.

It just took a call to the heating engineer (via the landlord) who came over and found that the revolutions of the pump were too high. He dropped them and the noise went away.

Sometimes a really simple problem can cause such a big headache!