A method and an apparatus for determining cooling fan speeds that should be avoided to prevent vibational resonance with system enclosures, given ambient conditions, and/or current geographic altitude. An exemplary method to determine one or more ranges of fan speed for one or more cooling fans in a chassis with one or more systems to avoid vibrational resonance in the chassis caused by the one or more cooling fans is provided. The method includes determining a range of operable fan speed for the one or more cooling fans that meets the cooling goal of the one or more systems in the chassis, wherein the one or more cooling fans are used to cool the chassis, and the one or more systems. The method also includes scanning fan speed for the one or more cooling fans over the determined range of operable fan speed, and collecting and analyzing read or write rates on a hard disk drive in the one or more systems over the determined range of operable fan speed. The method further includes determining one or more ranges of usable fan speed that avoid vibrational resonance in the chassis caused by the one or more cooling fans, based on the collected and analyzed read or write rates.