My family owns a single story house that no one has lived in for a few
months. It will be put on the market in the spring. In the meantime,
we've run into a strange issue. The house is 300 miles from where I live,
so I'm troubleshooting this from afar.

I stayed at the house during the holiday season and noticed that the first
time I flushed the toilet, the shower drain gurgled. I know that that can
happen if the trap is empty, so I ran water in the shower and then flushed
the toilet again. No more noise for the rest of the 4 day stay.

I should point out that the sewers on their street were replaced very
recently and you can see where they dug up the front lawn to attach
the sewer from the house to the new sewers. My dad and sister stop by the
house every now and then but I do not know if the toilet had been flushed
between the time the sewer work was done and when I flushed the toilet.
The assumption I made at the time was that the trap had been sucked
dry during the sewer work and once I refilled it, all was well.

Well, my sister just called and told me that she was at the house, flushed
the toilet (the first time since Christmas) and heard the gurgling in the
shower. She ran water in the shower, flush again and heard no more noise.
(She was not aware that I had had the same experience about 3 weeks ago.)

As best she could, she checked the trap in the basement and didn't see
any signs of leakage.

Since the house was empty for a few months before the sewer work was done,
and we don't recall the gurgling happening prior to that, I'm wondering
if the issue is related to that work. Could they have done something to the
sewers at the street that is causing a pressure related situation
and sucking the trap dry? Is a descendant of Daniel Bernoulli squatting in
the house when we are not there? ;-)