What does the speaker mainly talking about? What does the saying "you can’t hear yourself think" mean?

The sense of hearing is one of our most important means of knowing what is going on around us. We are warned of danger by sound. Sounds serve to please us in music. It has a waste product, too, in the form of noise. Noise has been called unwanted sound. Noise is growing and it may get much worse before it gets any better.
    Automobiles, trucks, buses, motorcycles, airplanes, boats, factories, bands—all these things make noise. They bother not only our ears but our minds and bodies as well.
    There is a saying about it being so noisy that you can’t hear yourself think. Doctors who study noise believe that we must sometimes hear ourselves think. If we don’t, we may have headaches, other aches and pains, or even worse mental problems. Noise adds stress to our society that already faces enough.
    There are two ways to cut down on the harm caused by noise. One is to cut down on the amount of noise. The other is to protect ourselves against the noise we can’t stop.
    Ways of making less noise are now being tested. There are groups for the prevention of noise in this country. There is even a law controlling noise. We cannot return to the "good old days" of peace and quiet. But we can reduce noise—if we shout loudly enough about it.