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2001 Silverado 5.3L with a tap, tap, tap or knock, knock, knock

If started and imediatly put in drive, a knock, knock, knock for 45 seconds. If let warm up for 2 min the put in drive, all good. Oil change every 3000, no drip, no smoke, dipstick covers 5 out of 6 holes, clean oil, oil pressure 40 at stop, 60 when driving. 135,000 easy miles. What is the knock?

Thank ya,ll


See if you can reasearch if this is one of the GM engines that have been indetified as being prone to piston slap.

It is more likely related to a non-harmful valve train issue.

What might be a non-harmful valve train issue?

Simply noise cause by a hydraulic lifter not performing optimaly,yes you are dealing with a under performing valve train but it is not harmful ,just distressing.