I have the same printer, which is now out of commission.  I talked to an authorized service person and they told me that it's a known problem with the mechanism and that it has to be sent to HP to be fixed.  They are replacing the entire insides for about $60 (a price the service person quoted).  Since ours was three years old, we just bought a new printer.

Eli & Miri Oren wrote:

 
My HP InkJet 660C printer makes loud "Klick" sounds and part of the printing is blurred.
While this happens on "Normal" and "High quality", the results on "fast" mode are acceptable (but still, the printer keeps klicking...)
Any idea what should I look for ?
                                                ELI OREN