David, Get a good mic, and put it in the engine compartment with yer laptop.

I did it on my car one day.. hehe

http://www.a-p-group.com/ashman/M104.mp3

I hope you track down that noise...

Alon

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'92 300CE - Sold
2004 C240 - 744 - C7 Wheels - Android Radio
2002 C320 - 816 - Sport Wagon - Sold
2006 E350 Wagon - 368 - Dead
2015 GL350 Bluetec - 197U