I would like to think that: vibrations do not come from thermal energy. A spring with two masses at each end of that spring do not vibrate due to thermal energy of the air around. That system vibrate because :when the spring is stretched, it creat a force pulling the two masses toward each other, but when the two masses are too close to each other, the spring create a force pushing the two masses apart. That process goes on and on,which is called vibration. So , fre vibrations of a system come from the own energy of that system.