If you say it's not the tensioners (how did you check them?) then it's probably the tensioner blades have started to break up.

I did the blades on my old S reg Scorp Cossie for a grand sum of £200 and about 6 hours on the drive way. parts needed to do it are here - not - i didn't replace the chains or the sprockets as they looked ok. http://www.fordscorpio.co.uk/timingchain29.htm

Fortunately my Y reg Scorp Cossie is silent