ETS 150/5 occasionally isn't smooth

[estesbubba]

I have an ETS 150/5 sander that's at least 8 years old and use it in my hobby shop. On some occasions when I run it, it isn't as smooth as it usually is. The last time it happened after changing from medium to hard pad. I checked and it seems installed correctly and the bolt is tight. Last time it happened, it was back to normal after a couple of power cycles, but wondering if something is starting to go bad? Is there any maintenance I can do to see if it goes away, or maybe best to just send it to Festool for a complete service?

 

[squall_line]

I believe the pads themselves have built in pad brakes, which I think are a rubber ring around the top.

I wonder if it's possible that they're getting dried out or hardened during storage, and loosen up/rub off the dry spots once they're running for a little while?