Noise suppression

Firstly, you made need something simple like a low-cost noise filter..that is a choke or an RLC (Resistor, coil/capacitor). If this sounds over your head, perhaps you need to talk with a hardware techie, or an engineer or electronic parts distributor.

Another such electrical/electronic means of noise *(static, hash/distortion) suppression is called an opto-isolator. https://en.wikipedia.org/wiki/Opto-isolator

Such opto-isolator noise suppression may be applications such as... ones that "are used to protect data lines while making RS-232/RS-422 connections. "
http://www.sitech-bitdriver.com/products/opticalisolator.htm?src=msn

Another, I believe this to be another type of technology, describes a different type of circuitry. this is the patent page but it gives you the correct idea.
http://www.google.com/patents/US6647367}
"An adaptive noise suppression system (ANSS) is provided that includes an input A/D converter, an analyzer, a filter, and an output D/A converter."

Zener diode also may work (transient voltage suppression diodes):

http://www.protekdevices.com/Assets/Documents/Technical_Articles/ta1001.pdf

I am afraid that you are looking at the wrong end of the problem. Once noise gets into a piece of apparatus it is normally not possible to winkle it out sgain. (Assuming that you do not know Harry Potwer ?P)
You must stop the electrical noise at source; i.e.stop that noise from getting out of the fan(s).
If te culprit is an older model with a brush motor it can be persuaded to keep its remarks to itself but you do need some learning. Might be possible to buy a mains-suppressor unit that is put between the mains socket and the plug to your unit.
If possible replace the fan with one drivn by an induction motor.
Ken Green

Simply said, that's not true.
I don't have the time to go over this with you. I suggest you check out all the links..one of them discusses what you're looking for in detail.

One of the expert regulars here..(nick is Engineer) might wander by and make a comment. I'm not volunteering him but he is far more expert than I am.

When you say the fans are causing the issue, are you sure that is true? The problem goes away if you disable the fans? Do you think the fans are inducing the issue inside the circuit or is it coupling with the wiring?

Without knowing what your system looks like, my first thought would be to try some EMI foil tape. If that helps, that is cheap and easy. You can buy filters that will take out high frequency signals, but it might also impact your hearing aid (knock out some of the sounds you want.)