1994 g 20 van 4.3 started hearing this intermittent knocking sound on started up only about 3 wks ago has to sit 6 hrs or so before it will do it again bought it with 69400 on it have 82355 put under 15 thou on it in the 5 and ahalf years i"ve owned it always change the oil 3000 or less once a year only drive 11 miles round trip to work always let it warm up whether hot or cold out dont seem to here it when i rev it up and down i baby the dam thing. snuck the dust cover open enough to feel if torque con bolts loose..not wouldn't a rod do it all the time ?? doesn't sound like a lifter. and when its running i go underneath and on the low end of the oil pan
9 the sump area ) i feel a small to medium vibration like the pump turning
9 of course ) and like the pickup screen could be hitting oil pressure is at op temp 13 lbs at 500 rpm and 35-40 at 2000 rpm haynes book says for v6 4.3 500 rpm 10 lbs 2000 rpm 30-35 been like this the 5 and a halr years i've had it that vibration is only at the sump area period

 

Sounds like it is piston slap. My 4.3 did it for years and never hurt anything, ran great.

 

THANK old chevy what do u think about the whirling like vibration on the oil pan sump ? to me not ever feeling oil pan while running (lol ) the knocking attracted me. you think the screen pk up could touching ??? thanks again