Because its cheaper to fix a bad CV joint than to replace 5 complete sets of wheels and tires, on the same car, that was already bought back for the same complaint! True story....they flew me and my FFT to another area to find out why the dealer couldnt fix the car.
As the cars got quieter and smoother, all the little things that used to be masked or ignored became the big complaint problems. No one had ever bothered to train techs how to figure out what component was the root cause of a problem condition. I was the supervisor on the development of the new (for 1994 model year) OBD II scantool. I had done a lot of work in the field, using spectrum analysis to find conditions ranging from radiator hose routing/shape issues to heater fan cyclic drone. (That turned out to be a cost saving manufacturing process where it was cheaper to produce the squirrel cage with a nice geometrically even number of blades, and of course the motor armature has to have an even number of segments for the two brushes. Unfortunately, the customers and many techs were convinced they were hearing a bad right front wheel bearing. You can put a lot of wheel bearings in a car, trying to fix the heater fan noise.)
Anyway, there was an opportunity to put better equipment, and better training, in the technicians toolbox. Those were exciting years for the techs, with OBD II datastreams to read and analyze, the FFT function, and a full breakout box kit that could look at cruise control, automatic a/c, and more. It even had an oscilloscope which could select from many different signals or be used with an autoprobe.
We put a lot of emphasis on understanding what is supposed to vibrate, and where the transmission path of vibration should not be. Radiator hoses, heater hoses, wire harness bundles, etc are really common mistakes made by enginners and home builders, for example. I can get real boring, so I will stop now.
Rob, PM me if you want to talk. I am still not certain this will be very clear in aluminum. Large blocks of aluminum often have thermoclines during the pour, which might affect your test results. Keep in mind, I dont claim to be an engineer...I just got stuck into the job because somebody had to do it and I think I looked expendable.
Regards, JimL