TomGeorge:
Hi,
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...
I was thinking of gluing a neodymium magnet and A3144E Hall Sensor.
Tube is actually SS304 which is oscillating (or going to) using electromagnet.