I started doing my own oil changes in the last year.I switched from conventional oil to Mobil 1 synthetic using a standard Fram filter.From time to
time I get a knocking sound on cold engine start ups.Any one have a idea why
this is happening.Thanks.

 

Used to happen to my 02 Tahoe also. There was a bulletin from GM saying it did no harm to the engine. Oh really?

 

I was using Valvoline full synthetic with dexos in my lacrosse with 3.6 vvt v6. Had a slight tick occasionally, used Mobi one full synthetic with dexos 3 days later catastrophic engine failure. Ran out of gas going down the highway when I restarted it was knocking severely and then engine went boom. Fr

 

I use Castrol 0-20W Dexos Full Synthetic in my Silverado with AC oil filters since new and have had absolutely no problems at all with it.