Hi,
Definately one of the sign of an upcoming shed.
But.
2-3 inches is a lot of substrate over a UTH.
Can you tell us what the temp directly on the UTH are? I ask because the snake can easily push bedding aside and come into contact with those temps.
That is why most people make sure that this figure is never dangerously high and use a thinner substrate so that the temps inside the snakes hide etc are at the correct level despite this.
dr del