DIAGNOSIS A mechanical obstruction in the scanner carriage track. Dust, a paperclip, or hardened grease can cause the noise.
FIX Unplug the printer. Open the scanner lid. Manually slide the scanner assembly (the black bar with the glass strip) from one side to the other. Feel for grit or binding. Use a cotton swab lightly dampened with water to clean the metal rail the carriage moves on. Dry it with a clean swab.
IF THAT DIDN'T WORK The scanning unit's drive belt may be slipping or misaligned. This requires partial disassembly to inspect. For most users, this is a service call.
HEADS UP Never spray cleaner directly onto the rails or glass. Liquid can seep inside and damage the CIS scanner strip, which is very expensive to replace.