2007 Buick Rendezvous makes loud growl after starting

The wife has a 2007 Buick Rendezvous that makes loud growl after starting.
Doesn’t happen immediately, sometimes it doesn’t happen at all.
I have not been lucky enough to have it make the noise when I have the hood up.
But from inside the car it sounds like it’s coming from the driver side close to the firewall.
I know “belt noise” when I here belt noise. This IS NOT belt noise.
Suggestions, sollutions?

I’m going to suggest the heat riser. The heat riser is a valve that diverts exhaust to help the engine warm up faster when it’s started cold.

Another possibility is the evap system purge system. It consists of a solenoid-operated valve that allows gas fumes stored in the charcoal canister to be drawn into the engine upon startup.

These systems can cause startup noises without triggering a fault code.

However, it could easily be just a resonance from a heat shield or some cover somewhere.

Awesome I’ll have both of those checked!
I was going to mention it didn’t happen when it was cold (the last six months) here in Michigan.
Is it easy to see if they are malfunctioning?

Whoever looks at it will first have to determine the sounds origin. My suggested causes are only ideas. If the shop is unable to duplicate the growling, the source might still be found by shaking things around. Heat shields, plastic covers, even plastic splash shields under the car might be able to be found loose and secured.

Good luck. These types of sounds can be hard to diagnose.

Timing chain noise is another possibility. I think on some engines the timing chain is positioned near the firewall. Ask your mechanic where the timing chain is situated on your car.