72 911T CLANGGING IN ENGINE COMPARTMENT

I HAVE THIS ANNOYING CLANGGING IN THE ENGINE COMPARTMENT OF MY 911T W/ MFI. MY GUESS WOULD BE THAT IT IS SOME SORT OF SWITCH IS ACTIVATED AT IDLE SPEED WHICH IS CONNECTED TO THE MFI SYSTEM, BUT IT SOUNDS LIKE SOME LITTLE GNOME IS IN THERE BANGING ON SOMETHING METAL. I DON'T REALLY KNOW HOW TO ISOLATE THIS NOISE, BUT I DO NOTICE THAT AS THE SWITCH GOES OFF AN ON AT AROUND 700-900 RPM THAT IT EFFECT THE IDLE AND I CAN FEEL IT MAKE THE ENGINE BOBBLE LIKE A SEVERE MISFIRE. I'M STUMPED. ANY IDEA/SUGEESTIONS
RADICALFIL
72 911T W/ MFI

Uh, you probably already know this and have checked it, but just in case -- CHAIN TENSIONERS!!! For your own sake do not run your engine if they have collapsed...the clanking noise could be that...