Here's some good info on cavitation and supports the explanation given by Bob et al

http://www.sunhydraulics.com/cmsnet/...1&title_id=288

There's quite a lot of heavy weight academic info on cavitation effects and the damage they cause to valve components. The file attached details a report that specifically mentions poppet valves and valve seat damage

Its probably possible to measure the vibration as a function of temperature caused by cavitation on the YS puel pump, if it exists...

Keith