1998camaross

I get this wierd rattleing/grinding noise on my tranny when I am slowing down and have the clutch in, at low speeds. This only happens sometimes. Also when the car is cold its hard to shift into some gears without geting a little tiny grinding noise mainly when shifting into 3rd. Does anyone else have this problem or might know what it is? When I bought the car it came with the billet Hurst shifter.