What causes yellow on oil dipstick an a clattering noise

I currently own a 2002 alero 2.2 160,000 miles an had oil changed two weeks ago. All of a sudden last night I was hearing a clattering noise in the engine department, so, first question was to check the oil dip stick, I check it an there is yellow stuff on dip stick. No it don't over heat, or anything like it would if a head gasket was to go. My question is if my water pump goes can it cause coolant to get in with the oil? Northwest told me yeah it's a major fix an that the noise is coming from there an causing the yellow stuff to get in with oil. But then other people are telling me no, usually thats a head gasket an when that blows it won't run. Now, i've checked the coolant resivore there isnt nothing in it, went to check radiator to see how low the coolant was but due to the radiator being under front car support its not visiable where the radiator cap is, I also checked for leaks but its raining outside.