Feels like beating the same dead horse over and over again but here goes:

https://www.dell.com/community/Alienware-Desktops/Aurora-R9-arrival/m-p/7388219/highlight/true#M18209

As @Anonymous mentioned, we would need more information of your system setup. It also helps to isolate which fan is making noise as I have posted in the link above.

OP,

Make sure your windows 10 is up to date. As well as your AWCC, and support assist. 

If you have a fan mounted on your CPU. The noise your hearing is normal unfortunately. 

* a push pull may not be possible if your using the Alienware liquid Performance CPU cooler. The hose going to the radiator is pre cut. So adding a fan would cause havoc on the CPU radiator hose. (Push, pull might be possible with a 120mm 10mm thick fan installed by removing top cover) 

The top cover is not coming off very easy without breaking the tabs. 

Ah, so I wasn't crazy when I thought the push-pull would be tough with how rigid the Alienware AIO radiator hose is. Thanks for the insight @Bmwpower603!

Unfortunately, the thinnest 120mm fan would be 15mm. I thought the R9's new "dome" top would have more clearance to fit a 25mm standard thickness fan over the top of the radiator housing, no?

I found one that’s 12mm thickness

https://www.newegg.com/p/1YF-0036-00001

But the radiator housing breaches the round part of the top cover.

Id guess there’s only up to 6mm in between the case and housing. (That’s towards the front) There’s  a lot more room towards the rear of the case. 

Yeah man, I bought mine a months ago, arrived like 2-3 weeks ago, with the liquid cooling option, and is SOOOOOO LOUD. I hate it for that. I don't think i will refound because all the others aspects but this little things make me think.. I will never buy an Aurora again. This is my second Aurora (the first one was an Aurora R4, and was silent AF). After 6 years (and many HW upgrades like ssd and GPU) I decided to take the NEW ONE. Well my impression unpacking this new R9 and booting it up is that dell is going low and low with the Alienware series..

Going back i would consider to invest on others alternatives but here we are, with this NOISY R9.

THANKS DELL. Make this machine NOISY

I wonder why some are so loud and others are not. Could it be hardware options? Mine has the i7 with a 2070 graphics card, 16gb ram, with liquid cooling. I have it on my desk next to my monitor and it's so quiet I have to put my head up next to it to hear the fans going most of the time. With everything set to max on Call of Duty Modern Warfare, the fans are audible but with my speaker volume at a normal volume I can't really hear any more than a slight hum from the fans. If the tower was on floor under my desk I wouldn't hear a thing. Thermal is set to Balanced.

@Anttero :

At what fps, resolution and detail level are you running CoD? It depends whether the hardware is pushed to its upper limit or not.

Well my resolution is set to 100% 2560x1440, FPS is set to custom, varies but I have been watching it and it's anywhere from 80-100FPS, averaging around 90FPS. All detail is set to the max. Refresh rate is 144, which matches the refresh rate of my monitor.

I have the same issue. The moment i start any game ihe top fan goes crazy like a turbo prop taking off. It has a GTX 2070 and CPU Core i7-9700 at 3.00 GHZ. I am not over clocking.

@RajYel :

Pics posted here will take a while for moderator to approve before other community members can see them.

Best if you have an on-screen-display program like GeForce Experience or MSI Afterburner that shows you how much heat and power is being drawn by both CPU and GPU when game is launched.