Just bought my 2002 suburban.Oil was old and low so l just changed it.It has 70,000 miles and l put a high mileage synthetic blend in it.When you start it up it sounds like a diesel.Only for the first couple minutes of driving then it quiets down.

Any ideas?
Mine is the LT 8.1 ltr V8...

Sounds like bad bearings in the engine. The previous owner had put heavy weight oil in it to hide the problem.

worn valve rocker arm,s or hydraulic lifter,s slow to pump up.it will sound similar to a diesel engine rattle until the lifter,s finally pump up enough oil pressure to close the gap,s caused by wear...have ur rocker,s adjusted/inspected for excess wear..change ur oil on a regular basis using a upper cylinder lubricant such as rislone.a product made by the schaler co..it will clean oil passage,s & prevent further wear..rislone is compatable with all synthetic & standard motor oil,s...do not use product,s like STP or MOTOR HONEY.they r designed to cover up the noise ..not remedy the problem....carbon build up & piston slap will cause a lower noise.not sounding as a diesel.what ur describing sound,s like diesel clatter.in gasoline engine,s most often caused by lifter,s or worn valve train component,s.

NORMAL CONDITION.

Here is the GM bulletin for this concern,#01-06-01-028A: Info - Engine Knock on Cold start up.

The knock noise is most often noticed during initial start-up
This noise may be caused by an interaction between carbon that has formed on the piston, the piston motion & the cylinder wall. GM Powertrain Engineering, & an analysis of engines with this condition, has confirmed that the noise is not detrimental to the performance, reliability or durability of the engine.
NO REPAIRS ARE TO BE MADE TO CORRECT THIS CONDITION.

valve lifters ticking do not worry bout it

sounds like Piston Slap to me. it was a common problem with the LS series motors. the tolerances between the piston and cyl. wall are out of spec. once you get the motor warm the pistons expand from their thermal properties and the tolerances get tighter and the slap or noise goes away.

pistonslap.com