2005 GMC Envoy XL rear banging noise

Something on the backdoor of my suv is making banging noise when started. My mechanic said it was blower motor or actuator or whatever. He fixed it. A few days later, the noise came back with longer banging noise in different tone and longer duration. My mechanic said ir was a faulty part. So he fixed with another part. It was good for about 4 days… then the noise came back… can you help me?

Was it an OEM part he installed? Some aftermarket parts don’t work well right out of the box.

check the cargo rails on the roof. If you have cross rails, one might be loose. I had a banging noise a while back on my van. It sounded like it was inside the side door, but was really on the roof.