Hi all, Ive done a lot of research over the weekend and today and come up with some interesting results. I was able to simulate the exact same noise that we have grown to hate in both cars sitting in the drive way but not to the same extent as driving over rough roads so i am 90% convinced its not in the suspension, rack or intermediate shaft but in the power steer unit.
The Electronic power steer unit or EPS is made by JTEKT a sub company of Toyota I believe. JTEK make all sorts of automotive stuff including the Torsen LSD in the 86/BRZ. The column P.Steer or C-EPS has / is used by countless brands and models including Toyota Corolla so i had a look at the 86 and my 2009 Corolla and they are 99 % identical, DAM. On the JTEKT web site i stumbled across some engineering publications and in these I found that they have been chasing an issue that they call rattle and back lash of the worm drive gear in the C-EPS, one artical also mentions inverse input, I.E input forces from the wheels over rough roads ( bumps)to the C-EPS and how the C-EPS dampened's these inputs via electronic inputs so the driver does not feel these input forces from the road at the steer wheel and that this dampening may increase rattle backlash over rough roads. They also mention in depth how they have tried to reduce this "rattle" and development is on going. So it seems that any car that uses this type of C-EPS has the potential to make this noise over rough roads. I have added a link if anyone would like some light reading, I will be seeing Toyota tomorrow armed with this info.
Click on the link
http://eb-cat.ds-navi.co.jp/enu/jtekt/tech/ej/index.htm scroll down to the blue journal, No.1009E 2012 Automotive Technology Special Edition, click the drop down list and scroll to TECHNICAL REPORTS then the 4th line down click on Development of rattle noise analysis...... there's also and artical the 2006 journal.
So it seems if we want this fixed we will all have to make a noise !!