"Empty barrels make the most noise" is a phrase which refers to how people with little to say are often the loudest.
The person who has the least knowledge on a topic may often be the most vocal person in the room.
This phrase make sense because if you hit an empty barrel it makes a loud echoey 'boom'.
If you hit a full barrel it will make a much lower-pitched and quieter noise as there is no space inside it for the noise to reverberate around in.
If you load a truck with empty barrels they will make a lot of noise every time you drive over a bump in the road!
Empty barrels are hollow, the space inside allows sound to echo around and effectively become amplified inside the barrel.
Conversly a full barrel has no space for sound to reveberate in so the sound will be far less amplified.
In terms of the metaphor, empty people, i.e people who have no real knowledge of a topic, are often the noisest for a number of different reasons:
Real barrels can be made quieter by doing the following:
Putting padding between your barrels will dampen sounds so if they do get hit, or they bounce off each other while in transit the noise will be greatly reduced.
Separating them will also prevent them from hitting each other when in transit thus reducing the noise...obviously, this requires a good amount of space in your truck or wagon.
Noisy (human) barrels are often hiding insecurities by being so talkative, avoid just shutting them down as this can make them feel even more out of palce and insecure.
Instead here are a few things you could do: