My three seismometers are on my garage slab and of course detect the 
change in tilt of the slab, vibration, an probably even electrical 
noise from the cars coming in and out. But it is really is not a 
problem as the signature is very apparent and it only obscures a very 
small fraction of the time I can detect quakes, so is not a concern 
for me. I am about 300 meters from the Pacific Ocean and the wave 
noise is my big problem. During storms in the Winter I may go for 
weeks when I cannot detect any quakes because of the wave-induced 
rock movement noise.

Richard, I am curious as to why this car noise is a problem for you? 
Do you want to just understand it, or eliminate it?

George

At 04:47 PM 1/7/2011, you wrote:
>OOOh ! I like this one.
>
>(no kidding)
>
>I got this trouble myself with an air conditioner coupled
>through the foundation slab.
>
>-----Original Message----- From: Karl Cunningham Sent: Friday, 
>January 07, 2011 8:56 PM To: psnlist@.............. Cc: Richard 
>Schneider Subject: Re: Engine Start/Shutdown Noise Spikes From Automobile
>Richard,
>
>Have you ruled out vibration through the floor of the garage? Car 
>engines produce significant vibration at startup and shutdown, due 
>to inertia of the flywheel and cylinder compression. When the engine 
>is running at idle these forces still exist but are much higher 
>frequency and mostly damped out inside the engine.
>
>You might be able to test for this by removing the magnet from near 
>the coil, and starting the car. It would then respond to magnetic/RF 
>noise but not to vibration. If you don't see the noise, then the 
>noise is likely from vibration of the garage floor.
>
>Karl
>
>
>On 01/07/2011 09:47 AM, Richard Schneider wrote:
>>Geoff,
>>
>>That all makes sense, but what is the explanation for *shutting down* the
>>engine and seeing a similar in amplitude spike occur at that very instant?
>>   At that point, the starter is not involved.
>>It appears to point to the alternator field collapsing on shutdown. BTW, the
>>start-up spike and the shut-down spike's have opposite polarities.
>>
>>
>>On Fri, Jan 7, 2011 at 7:38 AM, Geoffrey  wrote:
>>
>>>When you first start an AUTO like 50 or more amps
>>>might flow through the starter motor creating a large
>>>circuit for an electro magnet ??
>
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George 

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