Well had a mechanic use a stethoscope on the primary he's not sure what the noise is either lol. Wait and see if it gets worse I guess it's strange because it's not a metallic noise and the tension seems to be fine on the chain.

 

I had a similar noise and it ended up being a loose shifter arm. The arm was loose coming off the transmission output shaft causing the shifter link to rattle against the primary. Might want to tug on the arm to ensure the linkage is tight.

 

I would check for something else rattling in the area... They do make aftermarket chain tensioner that is auto adjust , maybe that is what you have, if it's not Oem. I have one in my 86 and been working great for years. Has a spring and uses the primary oil to maintain proper tension. Requires minimal attention once set properly.

 

I had a similar rattle in the same place and it turned out to be the compensator. The nut had loosened and it kept getting worse. It had to be replaced. Expensive. My mechanic said the primary chain was maxed out and it should be replaced. Might as well. $500 later the sound is gone.