See if you can find where they are coming from.
It sounds like it could be a carriage bearing.
get a magnet and see if they are steel.
check your x-rail for wear and move the head back and forth slowly and check for binding.
There are metal races in the x-rail that the carriage bearing ride on, these can be cleaned and lubed with a light grease, which will transfer to the bearing and then the x-rail race is cleaned again.