So I've recently noticed that overnight engine makes this knocking sound whenever you slightly tap the gas pedal with revs going up to 1,100-1,200. Higher rpm and idle sounds perfectly normal. But with added gas it sounds like Diesel engine. Anyway, once it warms up to operating temperature it completely goes away. Car has only 9k on the clock and has been trough 3 oil changes with the last being synthetic. Anyone else noticing same behavior on their engines?