Rear Airbag Problem on '03 Hummer h2

[Hummerguy32]

When i go out in the morning the truck height is very low in the back. Though when I start it up the airbags inflate and everything is fine for the entire day. I do not hear any hissing near the airbags. Do you think it's a small leak? a compressor going bad? Should I just say screw it and buy the strutmaster rear coil springs.... since I'm already going in that area to do the brakes/rotors

Any replies would be greatly appreciated!!