I have a Photosmart C4780 here doing that loud ratcheting noise when you turn it on etc.
Found the issue is likely due to a broken bushing on the lower right hand side near rear that supports the paper feed shaft.
Can manually move the shaft up and down a bit, and seems to have some broken plastic in that area.
A cleaning of the encoder strip, and calibration seems to have made it less, but the unit prints, scans and copies ok. So run it till the wheels fall off.