I was lucky enough to be able to extensively test all models and get paid to (as I work for a dealer) before I purchased my tractor. The inherent harmonic noise in the class IIs is why I chose a TC40D, which hardly makes any noise, cold or not. NH says the noise is caused by them trying to shove too much oil through to small of lines. Changing the oil to NH F200 or Amsoil seems to help reduce the noise. I have also found that keeping the Hyd. changed regularly helps also. As for changing some of the steel lines to hoses, I can't say I noticed that much of a difference.
