Bearing whine, rumble or drone, tapping gears and the rasp of poorly machined barrels. Tape transport motor and mechanism noise. From the perspective of the microphone, noise is noise. Find a good suspension mount and use a good microphone. Many of the camcorder supplied microphones are marginal in their ability to ignore physical disturbances.
Electronic attenuation is only good for lower frequencies and misses the higher noises.
Also by attenuating, you effectively cripple your rich sound foundation of lower response. You know that an ounce of prevention is worth a pound of cure -and like doctors, you're only doctoring the symptoms, not curing or healing the sound. Prevention is the only real way to go. A little equalization in post should be all that is occasionally required, though the very best audio people never need it. It is better to equalize at the source if necessary.