if it's a high pitched noise the primary heat exchanger has a buildup of debris and needs to be chemicaly cleaned or your inlet gas pressure is too high.
nik
January 2009
Sounds like the plate heat exchanger has had it. Also check your pressure should be 1-1.5 bar that might shush it up (but it probably wont hold). I had one of these and it sounded like a jet engine. Needless to say it's now down at the scrap yard these things are renowned for breakdowns.
mrplumb
January 2008
Automatic Answer
We may have found other answers which could help you.