I had 2x rev A in my 6610 and 1x Rev C in my 7450. There is very little difference between the Rev A and C to my ears. In both cases the 23k delta fan is whiny and loud even when running at low speed. The only real solution is to make the switch 2 RU as described in the fan mod thread with 2x larger fans + quiet 40mm fans in the PSU.
Is there a go to place to source rev c power supplies for 6610-48P?
I’ve had 2 of these for a while now with dual rev A in them, and it’s time to quiet them down a bit!