Royal Evo

I recently notice this weird grinding noise. It is not constant. Its intermittent. I started the car on flat surface and all is quiet and the car idles good. I step on the clutch on and off and nothing. When I backed out on my driveway, I hear this grinding sound. My driveway is on a little inclined. I found this video on youtube and its kinda similar sound. The evo owner noted it only happen when on inclined also. Here is the video. . What do you think is causing this? The sound is more noticeable on the passenger side, near the timing belt/alternator area.

Thank you for your input.

Royal Evo

BTW, I only have the Exedy single disk HD.