When releasing my clutch especially on an incline the noise from under my bonnet seems noisier like a rumbling.This gets noisier the steeper the hill.As the car pulls okay and the clutch easily holds its biting point i dont know why i am hearing this noise.
Not being a mechanic but having a little knowledge of cars I believe it could be the thrust bearing in your clutch. Nothing to be worried about really but it will get worse over time.
I go with rubberman for the release (thrust) bearing except........
the incline shouldn't make any difference.
With the car parked engine running and in neutral do you hear the noise when you depress the clutch pedal? Does the noise then disappear when you release the clutch pedal. IF "yes" to both then the bearing is most likely at fault. If no then we need to look elsewhere.