Sierra Matt

Probably the flapper valve as rocknfire says. Even though I have the 6.2L, I have the same squeak, so I took mine into the dealer and their comment was 'some do it some don't' and the official reply on my service invoice was "no problem found road tested veh could not duplicate cust concern'. Even though I can hear it squeak whenever it goes from V4 to V8 every time. Dealer told me that if they get a fix for it, they will let me know, but as of now, there is nothing they can do. Hope GM addresses it soon though, I know it doesn't hurt anything, but just annoying on a nearly $60K truck.

I am also having this problem. The dealer says that some do it and some don't, and that its operating as designed and since GM has not come out with anything on it there is nothing he can do. First new truck in 15 years, but I'm getting tired of the same response to everything.

I goy the RetraxPro with the wide rails. Cost $1540 from TruckChamp.com. Love the way it looks and works well. Being made from aluminum, I feel better about security. Only had to do minor modification of the GM plastic bed rails Om my 2015 Denali. It cost more, but looks great, works great and secure. I've run it through car washes with all the brushes and just a few drips get in past the seal.