Tom - you are a ventursome type. Good for you! Sounds like you made a good step forward for rehab-ing your pump. In general, the softer burbling sounds are high pressure sounds, whcih gradually fade away and get replaced by fairly sharp popping sounds.. that get steadily less frequent and quieter as pressure lowers. the last sounds which are comforting to hear are a small ticking.. sounds,as the pump settles down to the base pressure.
Generally speaking, it is the air in the pump oil that gives the softer sounds, so..as the pressure drops, you get a harder clicking sound as the oil get more and more gas free. But sharper sounds are consistent with a nice clean sludge free interior, too.
I think part of the sound can be the clicking of the reed valve. There is also a rocking of the rotors on the keyed shaft.. and that tends to become louder as the pumps wear.
Hope this helps some...
Dave Cooper
Created on Tuesday, April 24, 2001 10:21 PM EDT by David Cooper