As practical and useful as platforms and trays can be they do make more wind noise than a standard set of cross bars. There are some ways to reduce the noise coming from your platform, most of these will depend on which platform you have and the vehicle you are mounting it to but here are some options.
A wind fairing is the most straightforward way to mitigate wind noise. Brands like Frontrunner, Tracklander, Wedgetail, and Rhino either come standard with a fairing or offer them as an additional purchase option. In some cases, these are or can be vehicle specific so it is worth checking if you require or can get one that suits your model 4wd. It should be noted that while in most cases a fairing will reduce the noise you hear greatly it may not eliminate it altogether.
While not an option for all brands it may be possible to move your platform slightly backward on your vehicle to prevent you from hearing the noise being generated. Not all brands or all vehicles have this as an option, Yakima Lock n Load platforms are the ablest to use this technique but in some cases, other brands may also allow this as a possibility.
Mounting a lightbar underneath the front of the platform can not only improve your vision at night but also helps to reduce wind noise. It does this by blocking the air and obstructing the gap between your roof and the platform.