wraithkl626 wins this one; it appears that it was la bomba de agua . Cookie called me a few weeks ago and told me it was making the noise pretty consistently now. I went out and redid the belt-on/belt-off check, and the result was definitive that it was a belt-drive accessory problem. Based on the nature of the noise and what else had already been replaced, I felt that it had to be the water pump. I put the new one in today, and so far, so good.
Pros: noise gone, works fine
Cons: old pump didn't seem bad
Vehicle:
Chevrolet Lumina APV
