Fuel pump noise

One more vote for the cavitation theory.  I have seen these pumps, that are normally relatively quiet, scream like this when cavitating. One factor can be using winter blend automotive fuel on a warm day, which can induce fuel vaporization at the pump inlet where the pressure is the lowest.  If you are using Mogas it would be interesting to try some avgas and see if this reduces the noise.  I once did an experiment with avgas in one tank and winter blend mogas in the other and the difference in noise was profound.  I have often wondered if at least some of the problems Rotax has had with these pumps is actually caused by cavitation.  

You can make an experiment to convince yourself:

Temporary put small fuel can with a short thick hose directly to the pumps. Place the can at same level or higher than the pumps.
Your noise will go away.