Im currently finding that my internal fan is cutting out & or sounding like its struggling to rotate (my air con & heating are fine)

Then sometimes, it runs perfectly in complete silence, as if there were never a problem

Does anyone know why this would be or know how to rectify this please?

Im unsure how to get at the mechanism & wonder if its something I could sort myself?

Will it be expensive etc..

Many thanks in advance for any light shed on this