I would be wary of changing the attic airflow. If it's in a good equilibrium leave it. Especially if the current setup is soffit intake and ridge cap venting. Adding a gable vent could really disrupt things and create risk for mold, roof damage, etc.
You said new roof 2 years go. So, is it 1 or 2 layers of shingles now? If this past install was an overlay then you've got thousands more pounds sitting on that support structure. Adding some sort of bracing might do the trick, but it's a guess and I can see why contractors can't give you a clear answer for what the best course is. Hard to know without identifying exactly what movement is causing the noise. Could be rafters or joists rubbing on the plate as they shift slightly, rafters twisting, or anything really.
Also, go back in time and plant a tree that will now be big enough to divert the wind around and over the house