BBK,
amazingly I found my copy of the report in the first box in the loft.
The report is dated 3 September 1991 and the author was W.R. Hodson.
I think they were from a university.
When with the HEART at Wyton, I tracked down a report by Hoare, Lea and partners dated 30 July 1996 into a trial carried out on noise in the K . I do not have a copy of that report, but seem to recall it was performed at Marshalls. You mention a trial carried out in 1994, so that is at least three trials into the problem ! During my time on the K nothing was done to reduce the effects of noise on the a/c.