Amended:
Quackers, did some reading ... AFTER posting questions
but still some input would be nice.

What is the CFM capacity of the stock fans?
found this one, I think... 238.09
but then it further states 27.6W Power consumption, 4300 RPM, and 60 DB-A
(my S4 at stock is running at 3600 RPM and the rear howlers are 74 DB-A so my Android tells me)
I don't want to imagine 4300 ... there has to be some relief, no?

Any recommendations of replacement fans?

Considering Delta 1212SHE-F00 ... guess only as possible front replacement... (know this one, works on S5 very nice, 51 DB-A)

Read through Digi-key catalog for Delta Fans... This seems to come closest to the stock one...
Delta Electronics AFB1212GHE-CF00 (scary 5200 rpm), but wait, there is more ;-)
this one at 1ST PC CORP. Delta QFR1212GHE-PWM (6000 rpm, 210 CFM and wait for it ... 64 DB-A at a 'cough' 39 bucks).

Does anybody know any of these fans? PWM working of the QFR?
(AFB 4 pin Molex power and RPM sensor TAC output through its 3 Pin) I need to modify something here? (I really suck at modding)

thank you