" It seems to be coming from the left side (my left side when I'm riding) of the engine. It is fairly loud and increases and decreases with the engine rpms."

Well i was thinking valvetrain noise but when you said noise seems to be coming from left side of the motor could be an issue inside the primary.

If its valvetrain noise i recent had same exp with the 09 flhtcu i bought with 9,700 miles on that when hot had moderate valvtrain noise when running syn3 and or m1 bith syn 20-50 motorcycle oils.

BTW,i have exp with older classic cars motors running hyd lifters making noise with syn oil when hot too but when switching back to std dino oil of same grade the valvetrain /lifter noise go's away.

So with that in mind i decided to try spectro's std dino 20-50 bike oil and that cured the moderate valvetrain/lifter noise when motor was hot .

So since it's not that expensive to try and only takes approx 25-30 mins to change oil & filter give that a try to see if the noise goes away and if yes it was truely a valvetrain noise issue .

But if that doesnt get it done since you said noise seems to be coming from the left side of the motor maybe the issue is in fact inside the primary because the lifters & pushrods are on right side of the motor and rockers are on top of the motor which is where valvetrain noise should be coming from but you say noise seem's to be coming from the left side of motor & coming from the top or right side of the motor where valvetrain parts are located.

If changing motor oil to std dino doesnt get rid of the noise id try changing primary case oil to see if that stops the noise and if yes great,but if not its time to take to a known reputable HD or indy shop (or you if you feel like taking it on) to open up the primary to see if theres an issue with the chain adj and or the compensator etc.

Good luck and dont forget to post back what you find the issue is.

Scott