In my experience, traffic on the 101 also tapers off a lot after 10 pm or so. I suspect you'd hear some traffic noise but you'd have lots of ocean noise to mask it. You're probably more likely to be awakened by a train.
Whether you camp there or not that stretch of highway is worth driving. That whole part of the coast is like the backdrop of a car commercial.
I've lived here two years and when I come up out of Ventura and the ocean is suddenly RIGHT THERE it still makes my jaw drop.