Now for my response.
First: So, so, so, so, so. So. Stop saying so.
Second: They wrote you a very polite note. Avoiding confrontation by writing the note rather than talking to your face is the polite, kind thing to do. There is nothing wrong with that.
Third: You should do everything you can to mitigate the problem. If you are starting a loud STI with TXS exhaust at 4 or 5 AM and waking the neighbors, you are a dick. Quiet your car. My Legacy isn't quiet, but I also don't head out until 8 AM so it's hardly an issue... by that time, school buses are driving by.