DIAGNOSIS That's a classic sign of a major airflow blockage. Something is stuck in the suction path, making the motor work harder and louder.
FIX Turn it off. Start at the front: remove the roller cover and pull out the roller. Look for obstructions in the rectangular intake. Next, check the dirty water tank inlet on the main unit—sometimes a big clump gets lodged there. Finally, remove the dirty water tank and inspect the cylindrical filter for a thick layer of fine dust; rinse it if needed.
IF THAT DIDN'T WORK Detach the main unit from the floor head. Look through the clear plastic pipe on the floor head itself. Debris like coins or hair ties can get past the roller and jam in the pipe's bend.
HEADS UP Running it for more than a few seconds with this loud straining noise can overheat the motor. Always stop and diagnose the blockage before you burn something out. It's not designed to be a dry-vac for large debris.