Noises on some new planes (like ATR and A320)

Date:         12 Dec 96 04:39:32 
From:         "Damon Marcus Lewis" <dmlewis@mit.edu>
Organization: DML Enterprises
Followups:    1 2
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Hi, I recently posted a message mostly about the A320 in rec.travel.air and
asked if anyone knew what the loud dentist's drill type noises on the A320
and ATR were. Somebody wrote me and told me I should ask that question here
because there are a lot of really smart people who live here.


This is an excerpt from my original post:

There were a lot of high pitched noises (kind of like a dentist's drill) as
we were sitting on the tarmac just before departure.
Just before landing, and well after we parked at the gate [as in it was
still sounding intermittently as I got off the plane], the high pitched
noises came back again. They were much more noticeable than the engines
when they were on. As I deplaned, I realized that the ATR-42 sounded like
that too. I thought it was a *new plane thing* but I don't recall hearing
the noises on the 777. Does anyone have any insight on this?


Also, I am pretty sure it was not the flaps, the 440Hz power system, or the
fly-by-wire motor actuators (because I didn't hear them in flight, and I
can't see them being *that* loud).


Thanks in advance.
--
Damon Lewis