I upgraded my home server about a month ago.  I went with a Coffee Lake i7, Asrock Motherboard, and reused a modular EVGA PSU that I had from the previous build, and the fans and CPU cooler are also reused.

Everything works great, better than great.  It's running Unraid, has about 8 drives totalling 24TB with additional parity and SSD cache, and I'm running several docker containers and plugins.  All that stuff is great.  It also has another SSD that sits outside the array for a Windows 10 VM.

Here's where it gets weird.  Once in a while the computer will whistle.  Kind of like the sound a whistling kettle makes.  It only does it for about 2 seconds a few times a day.  I haven't been able to nail down where the whistling comes from.  The previous build never made a noise so I assume it's not the PSU.  The fans and CPU were also silent in the old build.

It's not overheating, in fact it runs a lot cooler than the last build.  It doesn't have a dedicated GPU.  It doesn't happen on a specific/regular basis.  Seems to be random.  There's no errors in the Unraid logs, and I have a few tools running as plugins and dockers to monitor hardware, so nothing being flagged their either.

Any ideas?