Simply replace the unfilled areas such as "" and "[date]" with your information.
I am writing to express my [feeling] about the [complaint] from your [source of complaint]. Your [source of complaint] is causing [detailed description of problem]. This is completely unacceptable.
The fact that you have let this continue tells me that you are either totally unaware of the situation or not a very good neighbor. I assume that you did not know that this was happening. Now that you are aware of the problem, I ask that you show respect and consideration to your neighbors by rectifying the situation.
As your neighbor, I will expect you to address this issue immediately.