What is wrong if your knees make a loud clicking sound when you walk but don't hurt?

There can be a lot of reason for that... some of them may be do to tight or loose ligaments/tendons, improper alignment, something wrong with the plica... it isn't normal to hear clicking, in the presence of pain or not. It may also be a meniscal tear, but you usually have pain associated with that. Meniscal injuries are frequently caused by "clipping" the leg, like getting hit in the side of the leg near the knee and you can easily get misaligned and tear the lateral meniscus.

If you have a good health plan, try to see an orthopedist, osteopathic physician, or sports medicine doctor. They can tell you if there's a problem.

ANSWER

If its regular and every time you walk its possibly a joint problem if its just when you start walking and it goes away, its nothing to worry about as that's normal as the joints have to stretch etc

Immobility can be a reason for this

inactivity is not good for your body, as an agoraphobic i know that well!

mine got much better when i, boo hiss, exercised, so you could try a little light exercise, stretching, a little jog here and there (and it got worse again when I stopped)

Lack of certain vitamins ans minerals can be a reason for this so making sure you are getting all the nutrients you need is a good idea

You should always talk to a doctor about anything that goes on in your body and about your concerns.