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Pump noise

I have always wondered why rotary water pumps can go from totally silent to 
quite noisy.  I have tried measuring both the magnetic rotating drive 
"thingy" and the "hole" in the coil.  Nothing definite there.  I now wonder 
if somehow the "shorting" coil in the potted drive electromagnet, develops 
more "shorts" and thus messes up the "rotating magnetic field."  Regardless, 
they get pretty noisy after a few years.  I also notice that the really noisy 
ones generally don't automatically start spinning the drive cylinder, but 
have to be "flipped" to start spinning.

HOWEVER - I can tell you of a relatively simple way to get a virtually 
totally silent AIR pump.  You build a box of plywood, 3/4" thick or thicker, 
with a "false bottom" that you fill with 10 to 20 pounds of gravel.  Then you 
"mount" the air pump on a 2" thick layer of ordinary unholstery foam (you can 
get it from any Fabrics store.) , run a soft silicone air line out through a 
hole in the box, run the electrical cord through a little groove you make in 
the lid of the box.  GLUE the box parts together, use sturdy screws to hold 
the removable lid on tightly.  Don't worry about the way the air gets inside 
the box.  Unless your worksmanship is a heck of a lot better than mine, there 
is ample air leak space between the lid and the body of the box.  Presto! No 
hum at all.  The box may still vibrate, enough that you can feel it with your 
hand, but so little that it does not generate the typical "air pump" hum.  
The pump does not get appreciably hotter than when running, noisily, in the 
open.  I got the idea from the old "Silent Giant" pumps - they are also 
filled with gravel.  

But, the darned gurgling of the air lifts is not stopped at all.   Unless you 
really slow down the bubble flow, which pretty much defeates the whole idea 
of the air lift. 

I live out in the country, and the hum from magnetic vibrator air pumps was 
awfully loud, compared to the silence of the rural night.  I would rather 
listen to owls and larks than humming pumps.

And, as far as I know, there is no debate potential in any Latin name for a 
"mass silenced" pump.  :-)