Ok I've just pulled the pan and Sharpe, you were right...the pump driveshaft was never installed...Lesson learned: never let someone else do the work for you...
...So now, how can I tell if the bearings are screwed?...In total the engine has run for about 5 minutes all total over a period of about a week with no funny sounds or troubles so I really don't think that there's a problem...but how can I check to be sure?
Thanks all!