A noisy toy is any toy that measures over 85 decibels (dB). You can download a free decibel meter app onto your smartphone to measure the sound of a toy. One of the most accurate sound level apps is the Armstrong Ceiling Solutions Sound Level Meter.
Noisy toys can damage children's hearing. When children are exposed to loud sounds, they become accustomed to loud as normal. But loud noise is not normal and not healthy for a child's hearing.
Here is the 2017 ACDHH Noisy Toys Press Release.
Remember that children often place the speaker of the toy right next to their ear. Some of the ways to make the noisy toy safer are to put tape over the speaker, make sure the toy is set on the lowest volume possible (some toys are adjustable), take the batteries out, place foam behind the speaker if possible, and limit time spent with the toy.
Other considerations include the environment in which the child is playing with the toy. Are other children present, and are they also playing with toys that create sound? The decibel level in the room can become unsafe. Exposure to 100 dB for 15 minutes will damage hearing.
The national Sight & Hearing Association conducts tests on the sound level of toys every year. This year they found many toys that are too loud. Here is their list.