My driver Door makes a loud distinct sound at only two points of the whole opening process. Once at like the first time you feel a bit of resistance, and second when you continue to fully open it, just before it frees up. The door doesn't squeak the whole way, just sounds like something's snapping in two only twice in the opening maneuver.

 

The plastic door retainers, give them a squirt of white lithium grease

 

GM's official name for that is a "Door Check" I think. (in case you try to do a search for it)

 

Check!

 

I have it too.
I tried lithium grease - it didn't help. But I didn’t spray aimed.
Door Check disorder does not interfere with the normal operation of the door. So I left the replacement for the future, for an indefinitely distant future.
It will be a problem when selling a car, the buyer will get the impression of an old unkempt interior. But until then, the sound will not kill you.

Oldblue, where exactly should lithium be sprayed? Mark in the picture, I'll try.

 

I just opened the door and with the little plastic straw attached to the spray can squired the grease over and under the plastic part that slides into the door pocket.

Where these arrows point, and inside the cavity

 

Thanks Oldblue.
When I get home, I will do it..
Now I am 5,000 km east, in Yakutia. But in a couple of weeks my work here will end and my Hippo is with me again.