Recently may car has been making a low pitched grinding noise. I only heard it in 4th and 5th gear at first but I can faintly hear it in all gears now. It is only when you accelerate, if I'm coasting I cannot hear it. It's mostly noticeable in 4th and 5th gear at highway speeds. Also if you rev the engine with the clutch engaged you cannot hear it, only when the transmission is spinning. Any help is greatly appreciated!