Fan noise in speaker

[FireLink]

Hello. I'm building a SPRO-2 based amplifier and I'm using three 12V/0,2A DC fans for cooling, but whenever I turn these on I can hear it a bit in the speaker. I'm using a 30W supply for the Pre amp for SPRO-2, and other circuits and I noticed that if I turn on the fans far from the boards(outside the final enclosure) and can't hear any interference. Does someone know if this problem is common, or if I could be solved with a better quality fan or a circuit?
Thanks in advance

 

[Netlist]

I don't know your amp, but perhaps you could add a larger heatsink to avoid active cooling?
How hot does it get without fan?

 

[PetruV]

put two inductors in series with the positive and negative of the fan then a capacitor in parallel with the fan,worked for me a while ago

 

[FireLink]

I don't know your amp, but perhaps you could add a larger heatsink to avoid active cooling?
How hot does it get without fan?

Unfortunately I can't change the heatsink

 

[FireLink]

put two inductors in series with the positive and negative of the fan then a capacitor in parallel with the fan,worked for me a while ago

How many Henries and Farads did you use? Thanks

 

[PetruV]

I can;t remember,the inductor had a couple of turns on a ferite core from a pc power supply and the capacitor was like 100 something uf