PLX 1000 Motor Sporadically Speeds up for a second

Hello,

I just got my first pair of PLX-1000s, both pre-owned. On one of them, the platter will speed up for a second about every 4 seconds. It will spin faster for less than a second then return to its original speed. I have asked the previous owner and they said they have never had this issue before so it seems to have started when it was shipped, despite it being in a road case inside a padded box. 

It is also occasionally happens at sporadic intervals and doesn't always follow a consistent pattern. Like sometimes it will spin at the right speed for up to a minute then will randomly speed up again and often falls back into the pattern (every few seconds). 

All other controls work and the problem remains regardless of what pitch/ speed the platter is spinning at. Any ideas as to what could be causing this and how I could try to go about fixing it at home? I would like to avoid getting it repaired due to the cost.

Thanks!

Gabe