Sudden new sound from flushed toilet

Our home is approximately 21.5 years old, brick 2 story, 3 bedroom, 2.5 bathrooms, city sewage. Within the last month our master bath toilet started making a turbine engine like sound when flushed. The second upstairs toilet flushing mechanism was replaced around the same time. Any idea why this sudden change in sound? Is there anything to be concerned about? Anything we should have checked by a plumber? We're baffled.