After much searching I found a fan that is very quiet and bought 2 of them :)
It's a Rasurbo 40mm 3pin fan rated at 19dba and does 4300rpm.
http://www.quietpc.com/gb-en-gbp/products/40mmfans
It's a hell of a lot quieter then the Akasa AK-160 BL-S 40mm Blue LED Fan
which while it does 5000rpm is an unnacceptable 23.97db so is at least twice as loud.
Just thought people might be interested.