If your knees sound like Rice Crispies...

I've got that going on - it's becomming my party trick to tell people to touch my knee and then I bend it.  Sounds like a sack full of glass.  Mine don't hurt either - although sometimes get a bit sore after long stuff (towards the end of 80 mils on my bike they were sore on Sunday).

I'm not concerned but I'm aware of it.

In the clinical setting, it is common to feel and hear the crunching under the kneecap.  This crunching, known as crepitus, is due to increased fluid under the kneecap and/or changes in the cartilage below the kneecap.  The initial crunching isn't related to pain because the tissue is not innervated by the nerves.  If no nerves are present, pain can not be felt.  All of us age and when you engage in endurance events, it is most likely that this crunching will develop.  The problem is when this crunching is progressive.  As the cartilage breaks down, pain can develop because the deeper tissue is innervated by the nerves.  As the tissue further breaks down, more damage can occur.  Some reports suggest that the lateral retinaculum (tissue on the outside of the kneecap) becomes irritated and painful.  Diagnoses, such as patellofemoral stress syndrome and chrondromalacia patella, have been used to label this crunching when it is painful.

In summary, you should not worry about the crunching but consider it your check engine light.  Sometimes if I see the check engine light of my car turn on, I continue to drive without assessing the problem.  As I continue to drive throughout the week and the month, I begin to notice that the car is not running well.  Eventually, it stops running and I'm sitting in the mechanic's garage.  My point is to assess whether there is a cause to the crunching before it can become a problem.  Many things, such as hip weakness, VMO weakness, increased Q angle and foot dysfunctions, have been suggested to cause the problem.

I wrote an article in a local magazine of Northern VA describing this issue.  Feel free to check out the following link:

http://90revolutions.com/injuryprevention/injurypublications.html

Check out the article, Patellofemoral Pain Syndrome:  What You Kneed To Know, under the magazine section.  I hope this clarifies. 

I'm not a medical person.

Personal experience has proven, if I'm stretching, keeping up with my yoga especially... My knees, and joints in general do not crackle as much or at all.

 Good stuff, thanks!  I knew it was crepitus, I just wasn't sure if it was a "bad" thing at this point.  I kinda figure that the break down process is going to be present for endurance athletes (particularly running).  I have been doing exercises to help with some of the muscle imbalances I know I have, so hopefully that helps!  Thanks again!