No idea but glad it's not only me.
I was paranoid for a while & thought I had a virus but seems like it's just a minor bug (I'm on MM - you too?).
Edit: Except for me it it's cloud downloads rather than uploads, but sure it's all part of the same issue.
It wasn't with google play music, I downloaded it on my computer, added it to my dropbox, and then download it from the dropbox app onto my phone and the actual cloud gives me notificationsYou can also turn off Auto-download as well in settings
2nd pic) if it doesn't stop then you can just shutoff all Google Play Music notifications in (Apps> Google Play Music) until there is a fix
Go to settings - -> general - - > apps - - > show system - - > now find smartshare.cloud - - > select notifications and block. Done! No more cloud notifications;-)
Uncheck this and see if it helps...if not there isn't really anything you can do without as I've said above instead of Turning off all GPM notifications doing the same to Dropbox App settings but problem with that is it will take away important ones too
A couple of others have said this on Dropbox Community forums maybe there will be a fix later on