the MSX6005 is an un-managed switch means, it has no internal management board and therefore there was no way to run any logic that sets the fan speed according to temperature. Because of this the fan always runs at top speed to make sure the unit stays cool.
It also might be that you have a defective fan (since you reported it also vibrates), so i suggest you also check in with Mellanox support and see if they can troubleshoot and determine whether you have a defective fan.
It might be that in the future the guys will decide to notch it down a bit but it is not clear if this is happening. If I hear anything, I will post.