You get your tires rotated and suddenly the brakes squeak, grind, or rattle when they were quiet before. It is a surprisingly common complaint, and the causes are usually minor and tied to the wheels coming off and going back on. Here is what is going on.
Pads and rust disturbed
Taking the wheels off exposes the rotors, and even a short time uncovered lets a little surface rust form; the first stops after scrub it off with some noise - see why rotors rust. The pads may also settle slightly differently in the caliper when the wheel is torqued back on, causing a temporary chirp until they re-seat.
Front-to-rear pad differences exposed
If the shop only rotated tires they should not have touched the brakes - but moving a noisier wheel position can make an existing pad or hardware issue newly noticeable. Sometimes a wheel that was masking a light noise is now on a different corner. The brakes did not change; the noise just moved.
A loose or over/under-torqued wheel
An improperly torqued wheel can cause vibration and noise that seems brake-related, and unevenly torqued lug nuts can even distort a rotor slightly, causing pulsation - see brake judder. If you feel a vibration along with the noise, have the lug torque checked with a torque wrench.
When to look closer
Most post-rotation noise is harmless rust and settling that clears in a few miles. If it persists, grows into grinding, or comes with a pulsation, have the brakes inspected - a pad or hardware issue that surfaced, or a torque problem. Keep pads and hardware in good shape with quality pads.