Cobber

Unfortunately mystery sounds are something that really need to be heard in order to diagnose properly. Maybe there is a knowledgeable forum member nearby that might be able to help.
It's also unfortunate that these days most mechanics couldn't tell the difference between their armpit from their arsehole without first having a sniff!
You may need to consult a proper specialist who knows these cars, I believe someone here will be able to suggest such a trusted specialist convenient to you.