2006 fast tapping on startup eases off some after warm-up. Thought it was timing belt tensioner but after inspection all that looked good. Hmmm.....noticed oil light flashing some after driving.....hmmmm hmmmm.....shut off engine and pulled dipstick. Got a pressure release sound. So....I think I have a cracked compression ring causing blowby and gas going past piston and into crankcase. That's causing oil to thin and oil pressure to drop and the lifter noise on startup. Has to be on rear bank because front bank compression is good. Didn't check the rear. Sound reasonable??? 244k miles.