Mutt, I totally agree... 747FOCAL should tell us what he (or she) knows about the RR 747/767!!
Mutt, for info, the 'widely known' noise readings I was referring to are published in the following report (see Figure 8 for the RR powered 747/767 noise results)
http://www.caa.co.uk/docs/33/ERCD0205.PDF
(dial-up users beware though - it's nearly 9MB!)