grating noise when shifting and not
 

I have noticed that I hear this gratin' noise when I shift from 1st to 2nd and back from 2nd to first. It sounds like the gears are grindin' but how is this possible if I have the clutch all the way down when shifting?

Also, I notice today, while comin' downhill, my foot was on the clutch all the way down, 1st gear in and was usin' gravity to basically carry me downhill. Then I start to hear the gratin/grindin' noise. I put it in neutral while still goin' downhill and the noise stopped.

I have been hearing this noise for quite some time now but haven't paid much attention to it:
1. because my old mechanic said my clutch is fine when I told him about it and told him to check it for me and
2. the noise went away until recently I started hearin it again.

I also hear this sorta clickin'/knockin' noise when I'm idle and my new mechanic told me that the clutch oil is low and needs to be replenished. the car is about 7 years old and I never changed the clutch oil or even knew you had to do that!

Could the problem of low clutch oil cause the gratin' noise as well?
And Is what my new mechanic tellin' me accurate?