Noises on some new planes (like ATR and A320)

Date:         12 Dec 96 04:39:32 
From:         "Damon Marcus Lewis" <>
Organization: DML Enterprises
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Hi, I recently posted a message mostly about the A320 in 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