Which country is this installation in ?

Poland. This doorbell is adapted to direct power from 230V.

OK, then you should follow the advice that others have already posted and get an competent electrician in to sort out the doorbell to remove the mains electricity from it.

At 240V this could potentially KILL someone.

Once that has been sorted out, then see if you still get the interference issue.

Check this out too for some background information on DOORBELLS

http://home.howstuffworks.com/home-improvement/repai...

Best you get a WIND-UP doorbell !!! ;->

http://www.dereve.co.uk/Dereve-Wind-Up-Door-Bells.htm

Just what is the round box? You have never really said! You have variously said:

In reply to a post by konrado5:

The round box is only phone box.

In reply to a post by konrado5:

This round box on the first photo is related to the doorbel (perhaps POWER).

In reply to a post by konrado5:

Phone cable is probably come in and come out from the round box.

Make up your mind! If you don't know, how do expect us to diagnose your problem?

If it a 'phone box', just what does it do? It's not a phone socket. Phone lines just don't stop dead without reaching a socket or some device or appliance. Please describe in much more detail just what it is and what it does?

According to my father it is phone cabinet. Phone cable come in and come out from this. I don't know if it is popular in Poland.

Edited by konrado5 (Sat 08-Feb-14 00:03:55)

So you are now saying it's a Block Terminal Connector like the UK ones half way down this page:
http://www.kitz.co.uk/adsl/btsockets.htm ? Does the phone cable on other side go to the outside of building?

In reply to a post by XRaySpeX:

So you are now saying it's a Block Terminal Connector like the UK ones half way down this page:
http://www.kitz.co.uk/adsl/btsockets.htm ? Does the phone cable on other side go to the outside of building?

I don't know if it is this type of Terminal Connector. The phone cable come in the round phone cabinet and come out of this left of the phone cabinet and come into the wall near the small rectangular connector. This rectangular connector is doorbell connector.

In reply to a post by konrado5:

The phone cable come in (from the R?) the round phone cabinet and come out of this left of the phone cabinet and come into the wall (to where?) near the small rectangular connector.

The phone cable comes in from the Right? From where? The outside of the building? Please make an effort to track it. We are not there we can't see it. We are relying on you to give us a full description.

The phone cable going into wall on L? Where does it go? Is it the cable coming from the L in your 2nd photo? Is that rectangular box your main & only phone socket?