Is it necessary to buy the sewing machine oil or will my air tool oil suffice?
More aboutoil noise noisy case fan
Make sure it really is the fan making the noise. I slow mine down to keep the noise low. Any light oil should work; I just put a bit of teflon based oil that doesn't gum up in mine from a hardware store.
Use a synthetic oil that doesn't leave a gummy residue when it evaporates.