if you do excessive running or you are heavy, more likely you
are going to suffer cartilage wear on your knees.
you can try taking Glucosamine supplements from Nature's Farm or
GNC, it helps.
i used to cycle and run alot. 
in the mean time, give your knees a rest, try to climb less
stairs.
Cartilage Injuries
Most cartilage injuries are due to impact or twisting
movements, and are more common in contact sports. Anyone can fall,
though, including runners and cyclists. Blows and falls can cause
cartilage tears. These can hurt, cause clicking noises, and may
make your knee lock on occasions. Cartilage can also become damaged
by accumulated repeated wear and tear, says American Running
Editorial Board Member Marvin Bloom, M.D.
Small tears in a meniscus may heal with rest. Menisci have a
variable blood supply, and in some cases healing can take months.
Larger tears and complete tears are more difficult.
Cartilage injuries need expert care. In many cases, a
conservative approach with rest and a change of activity works
well. The change may have to be permanent, though. Putting stress
on a damaged cartilage can only lead to more problems.
If surgery is needed, procedures vary. Some tears can be
stitched together and will then heal. Others may need fragments
removed. A very badly damaged cartilage may have to be removed
completely. Arthroscopic surgery involves small instruments and an
optical system inserted in your knee. You’ll usually recover
relatively quickly, and begin rehabilitation.
The worst part of cartilage injuries is the ogre of
arthritis. A damaged meniscus can grind on articular cartilage, and
damage it. The surfaces roughen, pieces may break off, and wear and
tear accelerates. The whole area becomes inflamed and swollen, and
the problem grows. The risk of arthritis seems to be higher after
surgery, but perhaps that really reflects the severity of the
damage in the first place.
http://www.americanrunning.org/displayindustryarticle.cfm?articlenbr=1692
http://www.wbcarrellclinic.com/Pt%20Education/articularcartwear.htm