Years ago while operating a very powerful ham 
radio transmitter I got RF into the furnace 
control circuits.  The furnace relays clunked on 
and off with modulation.  Possibly you are 
getting RF or voltage spikes into a dishwasher 
or washing machine and causing the water inlet 
solenoid to open and close, thumping the water pipes.
Charlie K3YA
-----Original Message-----
From: Dave Leddon <dave@xxxxxxxxxx>
To: Tesla Coil Mailing List <tesla@xxxxxxxxxx>
Sent: Mon, Mar 15, 2010 11:32 am
Subject: Re: [TCML] Thumping Water Pipes
At 04:04 AM 3/15/2010, you wrote:Â
>...  The discharge from the coilÂ
> was striking a ground pole which was connected to a ground rod
drivenÂ
> through the cement floor about one foot from where the water supplyÂ
> exits the ground and enters the garage.  When I grounded the strikeÂ
> pole to a different ground rod on the opposite side of the garage,Â
> the effect was greatly diminished, so I'm guessing that currentÂ
> passing through the pipe creates a magnetic pulse which reacts to
theÂ
> earths magnetic field but I thought that I would ask the experts
forÂ
> a more definitive answer.Â
Â
    I would think not the Earth's field, as such, as this isÂ
    quite weak.  Rather: enough current in a conductor canÂ
    change its size/shape: cf nagnetostrictionÂ
Â
But I thought that magnetostriction was a 
property that applied only to ferromagnetic 
materials and in my case the all of the pipe involved is copper.Â
Â
    This can result in audible effects.Â
Â
    bestÂ
     dwpÂ
Â
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