My Diesel engine is generally pretty quiet and smooth in normal use, however i was giving it some beans last night to clear it out and as the revs rise in the gears - the engine note changes distinctly at different rev ranges...probably goes through 3 distinct quite hoary notes. I assume its the timing changing as the revs build. (Pretty sure my Fiat did something similar)..... its one of the reasons i dont really like pushing it. I assume other diesel owners have noticed this???.