Could any A320 drivers comment on whether the RAT can be heard operating and if so, how would you describe the sound? I understand this may not be a common occurrence given the RAT is a backup system...

I understand its quite quiet! Particularly when it fails to deploy! LOL
Sorry couldn't resisit.
The sim sound effects normally try to be realistic, and I have never heard any aural evidence of the RAT operating.

I can only comment what sound it makes from the ground. I had an A319 pass over my house the other week, returning from an Air Test and the RAT was deployed. It sounded, to best describe it, like a microlight aircraft passing over.
When I have function checked the RAT operation on the ground, it is very noisy. Ear defenders are a must!
I found this video, which may answer some part of your question:

A320 Ram Air Turbine Test - YouTube (http://youtu.be/zx4BeNwQ-b8)

I launched one out several years ago for maintenance purposes and could hear nothing, but it was many years ago and I believe the new types have a bigger diameter which may make them louder. :confused: