There have been several posts about noisy 2009 systems. Mine included.
To be clear on the fans that are prone to failure... It's the ones at the ends of the CPU tray area.

. I initially thought just one of my fans were bad... Turned out to be both of them were making the noise....
The delta fans used look like high quality - probably just a bad manufacturing run... Either way... I ordered them from a surplus company for 4.50 each... Ended up getting a pile more as there is a minimum web order of $30.00. I have supplies to replace both fans 2x more if they crap out.
One more note... The only fan control app that can slow those fans to a "quiet level" is "fan control" not "SMC FAN CONTROL". This app was written by a MR member when we were dealing with max temps playing audio. Running those noise generators @ 600 RMP delivers a near silent machine... I idle around 36.9(c) which is well within spec. I have the fans set to kick up at 50(c)
Generally fans should have a smooth light drone to them... There was a definite light "thump" in each rotation that make it much more loud and distinct.