Thanks Guys for your suggestions.
There are no warning lights or readouts when this happens.
Temperatures here on the Gold Coast rarely go above 32 degrees C.
The sound does not occur at any regular RPM level.
It occurs at all different speeds including occaisionally soon after coming to rest. Sometimes when speed is being varied.
I get the sound intermittantly, sometimes once or twice on a 15km trip sometimes not at all.
The car is running perfectly.
Another small issue
After washing my car, usually late afternoon on a Friday the roof creaks rather badly. The next day the creaks are gone.
Obviously moisture is causing the problem and it dries out overnight.
When washing the car, after the iniyial drying off I will half open the roof and wipe all of the seals etc but this does not seem to help.
I noticed on this thread that some of you use a rubber compond.
If this is recommended what product can I buy in Australia?
Thanks you all again.