Since this happens at rest, it's defintely the front upper strut mounts (it happens when moving as well, you just can't hear it).
I just changed mine on Sat. The mount kits cost about $50 each from O'Reillys. They're made by Monroe and include the bearing as well as the mount - you need 2 kits. I also rented the spring compressor from O'Reillys: it was a $60 deposit which was refunded when I returned it (i.e. the rental was free).
Took about 3 hours, start to finish. Only 6 bolts (per side) hold the strut on.
Monroe have a page on how to inspect struts & mounts:
http://www.monroe.com/inspect.htm
If the mounts/bearing are gone, think about changing the struts when you fix this.