Hi,
zeus2kx:
How about a hall sensor?
I haven't used one yet.
It would be worth a try.
If the tube is steel, can you use a magnetic field type arrangement to detect the vibrations.
Even magnetize the tube and have a coil in the vibrating field or a Hall Effect device?
You would need to make sure you use an analog output type Hall device, rather than a digital output, as you may need to amplify a small detected field change.
Tom... 