Shaun's experience with them is the norm. They often are kinda noisy but otherwise innocuous.
The common spots that cause noise are the leaf bushings adjacent the vanes and the bakelite vanes themselves scoring the wall due to bearing issues. If a mainshaft bearing lets go, you'll start getting a higher pitched squeal.
I have pictures of what the pumps look like inside if you want to open it up. In my experience, once you open one and clean it out, you have to periodically open and lube them or they don't last too long. Also, prolonged periods of non-use can cause seizing issues.
Good luck.
