Hmm, the number of devices I used to run with covers off is in the hundreds.
Of course a lot of the covers inside a boiler are there for safety and
airflow reasons. However if one can localise the vibration and poke it with
a plastic knitting needle to be sure then you can power it all down and fix
it. The most annoying one of these sort of things was a tumble dryer that
squeaked, but only when the covers were on.That in the end turned out to be
just a belt, though to this day I do not understand why it sounded as it
did.

Old age in equipment does many odd things, as does disturbing things that
have been ok for years.

Back in the old days of the first colour TV sets, we had one that would
whistle very loudly sometimes and not others. That turned out to be a coil
on the timebase boared not vibrating at the real frequency it was using of
course, as that is beyond hearing but some lower frequency agitated by the
higher one. A blob of quick setting araldite fixed it. I'd not want to have
been the engineer trying to remove it from the pcb later on though :-)
Brian

--
----- -
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please!
"Harry Bloomfield" wrote in message
news
RJH brought next idea :
Couldn't see anything obvious. Some wire looms loose. But it'd take a lot
to create that sound. Another step is as you suggest - fire up without
the cover on - building up to that :-)

You will be OK with just the outer cosmetic, none sealed panels off. Under
that is a second room sealed panelling system, with out which it should
never be run.