Digital BW, The Print

When I run a nozzle check on my 1200 I often get a shuddering sound 
after the check and then subsequent checks are terrible, even if the 
intial check was ok.  A few cleaning cycles clears it up. I have not 
yet heard the sound during actual printing.  I have cleaned and 
lubricated the bar the heads travel on.  I have had the printer for a 
few years, but am happy with it and would like to fix the problem.  
Any thoughts would be much appreciated.  Again, it the "shuddering" 
sound only seems to appear during nozzle checks and cleaning cycles.  
(Only Click and Clack can accurately reproduce sounds.)

Steve