Usually aphids when I experience this. Look on the underside of leaves...young ones.

Hi Lycheeluva,
I had a similiar experience with my mango trees last year, and from what Jay has said, I belive it was aphids. My advice is to get a good insecticidal soap, or something similiar. My problem with the aphids led to sooty mold and it was TERRIBLE! I lost many of my tropical fruit trees, thankfully not my 'Maha Chinook mango!

Good luck,
Andrew

Do you see anything on the trunk/branches? You might have scale bugs. Unless you've seen them before you might not even notice them.

the only thing i found were these very small yellowish oval shapes about 2-3 mm wide and 5mm long, on some of the leaves- about 20 in total. when you scrape them off the leaves, underneath is a very slightly slimy liquid. i believe its a type of scale-
but despite long periods of intense gazing at the leaves, no signs of any moving creatures such as aphids. will take some pics of the patches of goo and of the scale if i find any more

Scale insects don't move a whole lot. I have a bonsai that was infested with them and I didn't know they were insects (they looked like patches of sap) until I saw one move after checking it for days.

Do a good coverage with horticultural oil. That got rid of my scale. Key phrase is "good coverage".

Did you see any whiteflys....small moth like bugs underneath? That is what is decimating South Florida currently.