im pretty sure that the fan inside your amp is cooling the audio driver board. it gets pretty hot under normal operation, and after a while the fan will start to deform from the heat and start making annoying noises. it will eventually stop working all together. this will cause the driver board to overheat and cause damage. you don't want that.
you can buy a new fan on ebay for cheap . just measure it and make sure you get the right size. it should be really easy to replace without taking the board out of the heatsink.