And chances are it will be investigated pretty quickly... you're likely to cause problems for more than just the next door neighbour's music. A friend of mine is a cellular radio technician and is occasionally tasked with identifying signal problems. Usually it's unintentional - some electronic device that isn't working properly, and they have tools to find the source relatively quickly and and order the owner to turn off and repair/destroy whatever is causing problems.
He said when nobody is home in the building that appears to be broadcasting noise, he will call the utility company and have them shut off power to the building to try to stop whatever is broadcasting.