I've got one of those little green Saer pumps. It seems a few people have had problems with them, but so far, mine is fine.
Certainly you can hear it, but it does not make enough noise to have to raise your voice if you talking to someone.
What it does do, is when the oil runs low in the tank feeding it, is alter its pitch quite a bit, and it does increase in volume a little. I'm wondering, is it the pump making the noise, or is what it is attached to acting as an amplifier.