I just dealt with this. Bought a certified '22 Tahoe in Oct. By Jan, "smoke" was chipping away on the grill. One dealer just west of Denver gave me the runaround about how I must have hit something, or drove through chemicals so not under warranty...AFTER telling me this was an "after market part" and therefore not covered by warranty. The service mgr was all "well we've never seen one in real life, because we just unwrap them off the truck and they're gone." umm no sir.
Anyway, I submitted a customer service ticket to Chevy, they found Autonation Chevrolet North who took one look at it and said "yeah for sure that's a warranty to make it right."
Long story long, if your car is still under warranty, get it to a dealer right away...and if they reject it, take it to another dealer. Or call Chevy.