At medium speeds there shouldn't be much difference between a 201 and 99/185, but they are different. The noise from the 201 mostly comes from the motor, needle punch and the bobbin can be heard turning at times. The 99 needs to be well oiled to have a smooth running hook and race, and it sounds different. At higher speeds there are a bit more vibrations, but mostly when you push against its' limits. The thing is that a 99 and 185 are much the same machine, I think the 99 might have a bit more cast iron to absorb noise.