It’s easy to bend a rotor, especially in transit, so spin the wheel while it’s still on the bike, and look for a kink. You might even notice the wheel coming to a halt at the bent part. If there’s a kink, carefully use a clamped-on adjustable spanner or a rotor straightening tool to fix it.
For a more precise check, remove the rotor and put it on a sheet of white paper to better show up any unevenness.