how to guess what the interference source it could be
I read about it and I found out that it could be our alarm system because the power is high and the transmission is constant so I run the technical support and they confirm, so I guess, problem solved. 

However, if someone else had the same issue and found that it was something else, please share :) I read it could be also the thermostat but couldn't find the specs of ours and unless it transmits also when it's not working, I don't think it could be that!