We live in a neighborhood where the 100-year-old houses are rather
close together. I bought the house (duplex condo), which had been
completely renovated, three years ago. Central air was installed in
both units at the time of the renovation.

This summer our neighbor has been complaining (loudly and increasingly
grumpily) that our two AC units are making too much noise and she is
having trouble sleeping at night. We don't notice the noise ourselves,
even though the units are right under our master bath window, because
the windows are new and do a good job of keeping down outside noise.
Her windows are not new, and she does not use air conditioning. When I
stand outside in our yard, I can imagine that it must be pretty loud in
her house.

She asked us to build a privacy screen around them, which we happily
did. But she's still complaining and recently suggested we bring the
builder back in to "fix" it. To which we politely explained that the
builder's warranty was only for a year, and it had expired over two
years ago. (Meanwhile, thinking to ourselves that it is odd that she's
only NOW complaining about this, three summers later!)

Questions:

1) Is there anything else we could do to cut the noise? Can I apply
soundproofing to the inside of the privacy screen? I am worried that
this isn't a good idea, since I figure AC units need lots of
circulation?

I would like to be a good neighbor, so if there is anything I could do
short of suffering in the heat, I will. Suggestions welcome!

Otherwise - 2) Legally, do we have any real obligation here? I mean,
should I just let the whole thing roll, and assume it is her
responsibility to put up a fence on her property, or install new
windows, if the sound bothers her? If so, how would you broach that
topic without making the relationship worse? (We are on fairly good
terms otherwise... it just seems to be this one issue, unless she's not
telling us something else is bothering her!).

jen