I also started hearing a similar noise. I used a long wood dowel to pinpoint the source. I bit down on one end of the dowel then touched the other end to different points. The water pump is the source here. I can hear that sound and feel it too at the water pump and in the housing on top of the water pump. Dang!! $400 for a water pump. But it's less than my old car payment :-)

__________________
1986 560 SEL
1960 Ranchero
1970 Cougar XR7
2002 Crown Vic Sport
1992 F150