Well I hate to say.. I wont say it, so I will just try to help.. #1 Fan driven power amps especially of the Pro variety have many power supply issues in home use, they hum, they POP very loud many times when turned on and off.. They hiss, and they do many things very hard to control.. Only crowns higher series like the K'series I think use like soft turn on and off relays etc.. They run dead silent and do not gain hum and ground problems due to the fan circuit stuck in the path pulling power and yes are fanless with some type of digital amp section that pulls less power and heat.
The only Way I have EVER heard a reduction on the hum with most Pro amps of this type are either using them on very low efficiency Subwoofer setups, but it still hums, only a little more acceptably, or by Using this convertor device in the second link below, which will cut it in half, but never totally eliminate all the noise that amp will create in the background
It is possible the ground Tie from the balanced is backwards in your wire, I believe #2 pin needs to be the Hot from your RCA, and the #3 and #1 Pins on the XLR must be tied to Ground of the RCA, check the Crown manual they should have a diagram, most do
. I have seen this occur with the Wire not being in correct phase and jumped to the right pins, but even if this is the case I still don't see it being completely eliminated. That is just my experience, as stated here a few times in this link
Link for Rolls Below RCA to XLR , this also adjusts the voltage in and out, and you can turn down the line input to reduce hum, but might not have enough gain out of the amp in doing this
Again I have been on this path and was never completely succesful in bringing down a Fan cooled amp to an acceptable silence level in home use. Good luck