2017 Sierra grinding after cold start

[Brand21]

Recently I’ve been noticing a grinding sound a split second after starting my truck. It only happens on cold starts. If the truck has been running then shut off and start it again there’s no grind. Sometimes the grind is little where you can barely notice and other times it’s louder. It’s almost sounds like the bendix in the starter but not 100% sure. I don’t want to go buy a new starter if it’s not the problem. Especially since a starter in Canada is around $400. Anyone else experience this? Or have an idea of what it is? I’ll post a video of the sound it’s making. FYI when I recorded this video, it didn’t make as loud of a grind as it usually does, but gives an idea. 

[Brand21]

[CamGTP]

Likely the oil pump, very common on cold starts in the winter months. These trucks use a variable oil pump system and the oil will leak down when the truck sits overnight. When started it takes a split second to quickly build oil pressure again and you hear the whirl/grind sound of the air/oil being sucked through the pump.

 

You can youtube video's of this too and hear more of it.