GMC Sierra Owner's Manual page 46

Keys, Doors, and Windows 45
Dirt and debris may collect on the sunroof
seal or in the track. This could cause an
issue with sunroof operation or noise.
It could also plug the water drainage
system. Periodically open the sunroof and
remove any obstacles or loose debris. Wipe
the sunroof seal and roof sealing area using
a clean cloth, mild soap, and water. Do not
remove grease from the sunroof tracks.
If water is seen dripping into the water
drainage system, this is normal.