The place where you use Ferrules on Campy brake housing is in the case of a split in the routing of the rear brake line. Like most frames of old had two cable stops along the top tube. Some not even that old. And Campy used to actually supply these ferrules with their cable sets, but no more, which bugs me cuz it's really hard to find the ones that fit campy brake housing (4.9mm) exactly. I have exactly 5 left in my stash. They are for applications like this...
The C60, unlike the C59 with a full length brake housing run through the top tube, uses the split method and cable stops. I didn't know that till basically, Tom's post.
Ya know... if the fit is good and the cable inserts far enough, you don't even need the ferrules and maybe the C60 is a tight enough fit in there for that very reason. I'd say the noise is coming from the edge of where it makes the bend as soon as it goes into the frame, so you're on the right track in finding it. And it probably isn't really that significant, right.?
I just like using the ferrules in applications like I pictured above. I think it just adds a little more "finished" look and keeps the ends of the cable from getting mangled. Also, inevitably the coatings on the end of the brake housing seem to shrink back a bit from the cut, exposing the wound steel of the brake housing, which looks gnarly if it's exposed. In addition, without the ferrule (which is very smooth), and a less than perfectly ground cut at the end, the bare steel can start grinding into the paint on the stop pretty easily as well. In the case of the C60, I think the cable inserts far enough in, and sounds tight enough, that it's a pretty good fit in itself.