It is often possible to distort and interfere with nearby sound systems by beaming high levels of RF at their system. This requires some knowledge of how it all works to allow you to tune for best results. For example, the amount of power necessary may be on the order of 50 watts or more, the most effective frequency to be used must be found by experiment (but is often between 20 and 30 MHz due to the length of their speaker wires), the transmitting antenna should be as close to them as possible without being seen (ideally it would be directional, but this isn't practical in many cases), and the type of modulation is a matter of experiment as well. If the RF transmitter and antenna are set up secretly, and the type of modulation is carefully chosen, then the target neighbors will not know what is happening or where the interference is coming from.
The major problem with this idea is that while you are transmitting RF you will also be interfering with every other user of that frequency around the world and the likelihood of the radio police knocking on your door is greater than zero.
I recommend using 100 watts at 26.9 Mhz to start with, using single sideband (LSB is fine) modulation and driving the microphone input with music from the album "Barcarolle, Famous Opera Arias and Duets". Tune the frequency first as this will have the greatest effect in increasing or decreasing the amount of interference.