What PSU do you have and what kind of surface is your case on?
The Z9 has a bottom vent so as long as your case isn't on a really fluffy rug that is blocking the vent it shouldn't be causing an issue. You can try turning it over and see if it helps, it shouldn't have a significant impact on the rest of the components.
Hi yeah just after i posted this thread i turned over the PSU and looking at it the surface underneath was NOT vented! Turning over the PSU has made everything all better and due to its side exhaust the case is remaining very cool. It was decieving at first as i never knew PSU's could make so much noise, or even had a built in fan curve!