Originally Posted by david s poole

what you are hearing is the beginnings of the 420 death rattle.the chain has stretched and when you drain oil it is also draining out of the chain tensioner.the noise you hear is the time period as the tensioner fills with oil and tightens the chain[about 4 secs] suggest that you plan on replacing chain and tensioner soon and check all three of the upper chain rails[one on the right and two on the left].