Bouncing Rigidbody

Hi all.

I am web developer and I am playing with unity for 2 months.

I have a self made 1st person controller. It is like the Rigidbody First Person Controller default prefab.
I have the same problem with the default prefab.

When the player is moving on a slope, or is in a "mountain" terrain, the object (in this case the player, but happens with any rigidbody object), it starts to bounce.

• Player (has freezy rotation) https://gyazo.com/e420b5e73558cfc7e4d1e43b4819eba2
• Object (has not freezy rotation) https://gyazo.com/212e81425a1fe5999a56706364fd8567

I think that I have the basic concepts, but I did not find the answer to my problem anywhere.
Anyone knows what is happening?

Thank you and sorry for my English!