holes are no longer round

HI all
I have been printing for several months now, everything has been fine until yesterday, when all of a sudden a noticed that holes and circles in my prints suddenly were no longer round but slightltly oval with little bumps on the sides.
I have not been able to rectify this by re-installing software, (I thought maybe corrupt files) and I actually have no idea on how to fix this. Has anyone else ever had this problem?

I have attached a semi blurred image of a small print with the problem

Belts too loose, gear slipping on X or Y axis stepper motor...

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Bob Morrison
Wörth am Rhein, Germany
"Luke, use the source!"
BLOG - PHOTOS - Thingiverse

Quote
rhmorrison
Belts too loose, gear slipping on X or Y axis stepper motor...

Thanks, it was exactly that!
Y belt stretched, due to the fact that I cant get my bed temperature up to 110 degrees, so I tried to (temporarily) close in the bed to help raise and maintain temperature, it worked but ended up causing the belt to stretch due to the heat.
problem solved