If you have a 2020.5 – 2021 Travato you may be able to stop the vibration by moving the front roof rack bar further back.  Or, you can install an air dam in front of it.

If you have a 2022 or newer Travato you would be better off just removing the front bar or putting an air dam in front of it because the rack mounting will be in the way of trying to just relocate it.