I suffered the same problem of noisy fans with my ARC 120's & 150's and cured the problem by replacing the Taiwan made original fans with those made by Pabst, Germany. They are widely available in Europe.
I just bought fans covers for my ARC 610T's because I have inquisitive grandchildren and would not like them to touch the hot valves and I noticed the fans fitted are made in China but are very quiet - so far!
I just bought fans covers for my ARC 610T's because I have inquisitive grandchildren and would not like them to touch the hot valves and I noticed the fans fitted are made in China but are very quiet - so far!