Do corals react to sound?

This morning one of the fans on my lights was making a horrendous noise. It stopped after I gave it a good tap - but my corals all remained closed up for a long time and are only now starting to open up.
Is this coincidence or were the corals reacting to the noise of the fan? Could the sound have been sending vibrations through the water? The lights still came on at the usual time and the sound only lasted 2-3 minutes maximum...

Cheers,
PatD