How can we reduce loud server fan noise during daytime updates?

Fans often run at full speed briefly during POST and hardware self-tests, regardless of normal workload. Acoustic treatment will not eliminate that burst. If the noise is only occasional, schedule firmware updates and reboots outside office hours or use automated, cluster-aware maintenance. If the servers are loud for long periods, measure the peak level and have an acoustics professional recommend a properly engineered solution.

First check whether the room is getting warm or whether the new servers are using an aggressive thermal profile. Improving airflow or cooling could prevent fans from ramping up under load. Some systems also have balanced, quiet, or sound-limited fan profiles, but test those carefully because lower fan speeds can mean reduced performance or less cooling headroom.

An acoustic cabinet designed for rack equipment could help a lot, especially if the servers are located in or near an office. Wall and ceiling treatments may also reduce reflected noise, but make sure any panels are fire-rated and suitable for a server-room environment. Do not enclose the equipment without checking airflow and cooling requirements.

Treat this as a facilities and building-acoustics issue rather than something IT has to solve alone. Facilities could measure the sound, check the shared wall, install a heavier door, improve the wall construction, and verify that ductwork is not carrying the noise into the neighboring office. Cheap foam panels alone usually will not stop much of the sound from escaping.