What causes a slight ticking noise from the engine when first starting up

Hello, what engine is in your GMC truck? Ticking can be simple fuel injector noise, or could be the sign of valve train concerns. Either way you look at it, it'd suggest having a local technician near you who is experienced in hearing what is normal and not have a listen. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops