Probably not. It's just that making the 24-70 silent was not a priority when it was designed. For most of the time SLR cameras have had auto focus lenses the emphasis has been on speed. Video only really took off in the last decade or so. AF has been widespread in the SLR market since the late 1980s. The newest version of the 24-70 f/2.8 from Nikon was released in 2007. Although the Canon 5D had been out a couple of years and was in the middle of revolutionizing the whole concept of shooting video with a DSLR, Nikon did not have any DSLR bodies available at that time that shoot video, and probably didn't expect to offer a DSLR body intended for serious video work any time soon until the lens was already very late in the development process. Even then, the serious videographers using DSLRs for commercial productions were sticking with manual focus, and still do.
Not being a Nikon shooter I can't tell you how the AF speed of your Nikon 24-70 lens should compare to your Canon 18-55 IS STM, but I can tell you that within the Canon product lines the STM lenses are generally a little slower than their USM counterparts that are about the same size and have the same amount of glass to move when focusing.
There does come a point, though, where the much larger and heavier USM lenses require longer to focus if the heavier lens elements that move during focusing have to move a significant portion of their total travel. Any full frame 24-70 f/2.8 has a lot more glass to move when focusing than an APS-C only 18-55mm f/3.5-5.6.