Oh Mario, Oh Mario.
I'm so sorry about your tach problem. I had the exact same thing happen to me. First I lubricated the cable. No impact. Then replaced the cable, no impact, finally, I sent the tach to speedometer.com, Rick Borth. Should be less than $100 to refurb, and you will be thrilled. The noise is coming from the inside of the tach, and no external lubrication will be effective.
Here's the rule on Pagodas. If you have to take the instruments out, you should do as much as you can in Preventative maintenance, since it is such a bear to take out the instruments. new gauge seals, refurb tach and speedo, new cables, replace bulbs (consider LED's) for brightness without heat.
Good Luck.
Mike Mizesko
Columbus, OH