Douglas,
I used the term that I understand the Brits use for back pressure release (not backfire!). Some back pressure is good in order to create suction that draws off spent gases, and it makes the noise I referred to. What I refer to is a healthy burble you would expect from a properly timed engine when the throttle is closed from a high RPM. Sorry if I implied that Carling is ill.
As she lives in Sarasota and the GT40 is firmly entrenched in France, there will likely not be a pic of them together any time soon. As they are both red, it would make a pretty sight...
Trice
1968 280SL US, signal red/bl leather, auto, kinder
Sarasota FL; Alsace France