This is true for ice, but also for other materials. So ice is slippery because of this layer of water which is always there, regardless of pressure or friction. This has to do with the fact that the water in the glass is warmer than the ice cube. The cube gets warmed by the water, first the outside layer. The warmer ice wants to expand, while the inside is still small and stays the same.
Cracks form inside the cube where the expanding ice breaks loose from the inside part.
That is what you hear, and you can see it too if you look closely. So it should make a difference whether the water in the glass is really really cold, or if it is warm. Same for the ice cube. There will be a difference between a cube straight from the freezer, and one that has been sitting on the kitchen counter for a while. Here's the correct explanation , in a story from the Exploratorium about ice hockey, zambonis and all that.