Silencing a 2u case - CPU fan recommendations?

Hello, I have a 2u rack mounted case in a studio. Standard dual core AM3 processor, not overclocked, used for music production.
The case has 3 x 50mm fans in front intake. Ive managed to find Fractal Design 50mm fans that are silent. But the processor fan is too loud.

I have a Gelid Solutions Slim Silence Low Profile AMD CPU Cooler, and it is far from quiet.

The case runs quite hot anyway due to the design so I dont think acoustic treatment is an option.
Can anyone recommend a quiet/silent AM3 CPU fan?
Thanks

You said it yourself "The case runs quite hot anyway"... The faster a fan is designed to spin the louder it gets. The low-profile heat sinks have less heat sink area to dissipate heat so you need a faster fan. Maybe something like this will work:
Quiet-Low Profile Fan