Help diagnose strange throttle sputtering noise
 

I`ve got this annoying little noise at mid throttle that is coming from the CIS area on the engine. I think sputtering is the correct term to describe it. It sounds like shaking a crankbait with a little bead inside, for those who fish...But this is not detonation, I run 93 octane, my advance is at factory specs and it definitely comes from the CIS/throttle area. I have also noticed my gas mileage has decreased, but power feels about the same. Something is going on in there. What could it be?
I adjutsed the valves and changed the oil last week-end, but I do not see how this could be related. Other difference would be that the weather is cooler now.
Any ideas?

Are you sure the valve adjust is correct? Could be a little tight on a valve causing some reversion. That would explain the lower gas mileage too.

I`ve never heard what reversion sounds like, but you may be right. I will look into that possibility.

Reversion (mixture flowing back into the intake) can rattle, or other strange noises. It all depends on the intake system and amount of reversion. Seems as the best guess tho considering the recent work and symptoms. Also may want to check the CIS and make sure everything is in ordnung. Maybe a loose bolt or something.

That means one of my intake valves would be too tight. Easy to check, no need to drain the oil. The noise could be the air metering plate fluttering around maybe?

Yep on both counts. Intake valve is off or maybe a loose ??? in the CIS. Air metering plates make some weird noises, had a VW with CIS that howled and also did a lip-flapping noise (like imitating a horse) due to a funky air plate.

Update: I readjusted my intake valves, the engine runs fine, but...the noise is still there! It is a screeching noise, which seems external to the engine. Now, I noticed my trip odometer is dead, so I am wondering: could it be the noise of cable teeth grinding in the gearbox? Has anyone experienced this kind of noise associated with odometer failure on a 78Sc?