What model boiler is it?
Sometimes howling or hooting (I have heard people say "it sounds like a ghost!") can be down to combustion problems in which case you definitely need an engineer.
Could also be something vibrating or rubbing, or maybe a fan on its way out. Occasionally flues can cause this noise - it's natural boiler noise but that particular flue configuration amplifies the noise.
Bunslinger
May 2009
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