i need help to figure out this:

i have aliases of the kind something/something/something
the rss feed only substitutes the last part of the alias.

for example, an alias of /pets/dogs/doberman :
the feed for /pets works, which is node/(nid)/feed
but the feed for /pets/dogs is /pets/node/(nid)/feed which does not exist
for /pets/dogs/doberman is /pets/dogs/node/(nid)/feed

any ideas of where to look?