97 blazer knocks until warmed up

[bluebuick91]

Every time I fire up my 97 4.3l blazer it knocks and taps super loud until it warms up a little. Every morning I hold my breath. And its only on first start. After it has been run there is no noise. Why is this happening? Is something failing? It has over 100,000 miles

[jerryg2112]

How old is the oil and filter? How is the level?

[bluebuick91]

The oil and filter are fresh I change it every three thousand miles level stays the same doesn't use or burn it between changes...now upon a recommendation from O'Reilly s worker a synthetic oil was used along with mystery oil additive. Was no change in performance with them so have switched back to reg 10/30 oil no additives.

[DeltaP]

Depends if the noise emanates from the lower end or upper end of the engine. Oil pump failing or valve train, stuck lifter noise.