Wind Turbulence on Windshield

the g.m bug shield would sometimes cause that if it's gm shield take it back, buy a smoked lund and make sure there is not a riser at the back only straight, it makes the wiper flutter and sounds like rock or sand hitting the glass.

I've dealt with that noise about 100 times at the dealership. Almost ALL bug deflectors can cause this issue. It is a common issue with the new style trucks and was also a common issue for the first 3 or 4 years on the old style trucks. The noise is caused by the windshield reveal mouldings on either side of the windshield vibrating against the windshield (due to the change in airflow caused by the deflector). the best fix is to loosen both reveal mouldings and apply a small bead of silicone (black is better so you won't see it as much) to the underside where it contacts the windshield and then re-install it. once you've done that, remove any excess that has squeezed out and allow to dry for about an hour. another thing to do it completely remove the reveal mouldings and apply double sided tape to it where it contacts the windshield. just remember that when you replace the windshield, the noise will likely come back. This is the best (an actually recommend GM repair) for this issue. If your wondering what the reveal moulding is, it's the hard plastic at either side of the windshield and held on with, if i remember correctly, 6 torx headed screws (which you will see when you pull back on the weather strip that runs from the front along the top to the back of the vehicle).

What kind of silicone do you get?

It’s called black silicone sealant sold at all auto parts stores. There is only the one black sealant they sell so you don’t get confused with another sealant