We just got our sprinkler system winterized today, and shortly after when I flushed the toilet, the pipes made a crazy loud groaning sound. I did it again and observed the pipes in the basement and the main line was vibrating a lot and making a crazy squeaky noise. It even happens to a lesser extent when I run a sink (not after, but during, when water is running). The irrigation guy only messed with the sprinkler line next to the main line and he said he's never had something like that happen before. Any idea what's going on?

did the sprinkler man blow air into the pipes to winterize them?

Yup, he did. What might that have done to the other pipes?

a little air in the system will do no harm.
it will cause some of the symptons you describe (banging and vibrating) but it should quicky be expelled when you open some faucets.

High pressure is used to rid water and moisture from your sprinkler, no one looks at the pressure gauge as they often want to get in, do their job and get out.

The air pressure got into your potable waters and should be removed when you open a few faucet.

Best Wishes