knocking 5.3litre engine

Shortly after I start my truck the engine starts to knock quite bad. Once it warms up a couple minutes it stops. The longer it sits without running or the colder outside the worse the knock is.
The engine has 170,000 kms and has done this for about the last 10K. The oil pressure seems fine and I change it every 5000kms. It has tons of power so besides this noise evrything else seems normal. I was told by a couple people this is not uncommon in the 5.3l. Something to do with alum parts in engine. Any help or suggestions or comments? Thanks

They're known for piston slap.

All engines will experience this after alot of miles or an abusive driver. They sound like they need to be adjusted and some engines have little hydraulic lifters that go bad and it takes them time to build up pressure. On the rod type you have to adjust the valves until the are firm. Hope this helps.
Jacob