It’s hard to answer this unless we determine what ‘audible’ means. And please don’t forget that the total noise floor in your studio is a sum of all fans and other sources. The H9000 will add to that.
I had a MacPro 2019 with a 16-core Xeon here in the studio, and I found it to be very audible under load even with my 50 years old ears.
Then, I have the new generation RME M32 Pro A/D and D/A converters which have very noisy fans unless you turn them into silent mode, which is only suitable for a cool a/c environment.
Not to mention the Moog One 16 which sounds like a jet turbine on idle 🙂
That being said, the H9000 fan is audible. If you plan to have the unit directly in front of you, you will notice the fan. If you have it rack-mounted, let’s say in a wooden rack, and have the rack full with gear (no gaps), you will not hear it even at close distances around 30cm.
There is another fantastic option though. Since you will most likely end up using the H9000 remotely, you can place it virtually anywhere in your studio, your house, or even in your neighbours house! Unless you use ADAT ( I wouldn’t recommend using this outdated format due to the channel limitations and inconvenience), you can easily install it up to 100m away, using MADI or AVB lines. Then, it is ‘dead quiet’ for sure.