RV Slide Out

[mowerman camping]

I have a 2019 Coachman Catalina Legacy Addition pull behind. Every time I let the slide out out it leaves grease behind on the inside floor. It appears to be operating as it always have since new. The grease is only on one side, the side closest to the rear. I have never put grease on the slide rails. Does anyone have an answer ? Thanks in advance

 

[Wemustrv]

Could be coming off the roller wheels