You're in the middle of a workout, powering through your first squat, when suddenly you hear it — an unsettling crack. Or perhaps you're not even exercising, just walking up a flight of stairs. And maybe it's not quite a crack but more of a click or pop, and it seems to happen a lot.

It's not the first time you've wondered whether you should make a doctor's appointment or just shrug the sound off. Could cracking knees be a sign of arthritis? Or is this just a harmless quirk of the human body?

"The knee is really interesting because you have two portions of the joint that are weight bearing and then you have a floating bone in front of it," explains Dr. Jonathan Zalamea, a sports medicine physician at Houston Methodist. "This makes for a complex structure, where it's not uncommon for things to go wrong."

When this joint is making noise, is it trying to tell you something?

Why knees crack, click and pop

The knee is the workhorse joint of the body. Not only does it need to be strong enough to support almost all of your body weight. But it also must be flexible, acting as the hinge between your thigh and lower leg that allows you to walk, run, bend, squat and more.

Just like a door's hinges might start to creak after years of use, knees can develop a bit of a "creak" too.

The most common reasons for knee clicking, cracking and popping include:

• Air bubbles – popping of gas bubbles within the fluid of the knee joint
• Irritation under the kneecap – when inflammation occurs in the space between the kneecap and femur, it can increase resistance in the joint and cause knee components to make noise as they move
• Wear and tear of cartilage – if the surface of cartilage has become very rough, the surrounding knee components move less smoothly over it. Dr. Zalamea compares it to driving over one of Houston's many potholes to explain why this leads to cracking sounds.

While all of these can produce noise, not all are cause for concern.

For instance, air bubbles developing in joint fluid is totally normal. So is when they pop as the knee bends. It might sound cringey, but this is completely harmless.

When should you worry about noisy knees?

How can you tell when knee cracking, clicking or popping isn't harmless? Dr. Zalamea recommends being on the lookout for the red flags that signal there might be a problem.

"If noise from the knee is accompanied by pain, swelling or movement limitations — such as locking or catching sensations — that's when we get concerned," says Dr. Zalamea. "But if the knee is just popping and there's no pain, we're not worried. Some people just have noisy knees."

In other words, it's more about the sensation you feel rather than the sound you hear.

"If every time you go upstairs — yes, you hear cracking — but you also feel resistance, like sand in a gear, or discomfort, we start to think about patellofemoral syndrome or knee osteoarthritis," explains Dr. Zalamea. "Or if you have to kick your leg to unlock it, that's when we worry about a structural problem, which is definitely something we want to address sooner rather than later."

Patellofemoral syndrome is one of the most common causes of knee pain. It occurs when the space under the kneecap becomes irritated and inflamed due to repetitive stress, improper mechanics or muscle imbalance. (Related: Is Your Pain Just Muscle Soreness or an Injury?)

"Leaving issues like these unaddressed can lead to bigger problems down the line, sometimes even serious injury," adds Dr. Zalamea. "We always want someone experiencing knee pain to come in for evaluation so we can identify and treat the cause."

How to stop your knees from cracking

An unsettling noise might be what brings the issue to your attention, but the main reason to take action is to keep an underlying knee problem from progressing.

"Usually, I'm telling someone they're dealing with patellofemoral syndrome or maybe knee osteoarthritis, but either way the treatment is typically the same — something for the inflammation and something to strengthen the muscles around the knee," explains Dr. Zalamea. "Many people think I'm going to tell them to stop exercising, but it's actually the opposite."

Correcting knee pain isn't as simple as taking a pain reliever and giving your knee some rest. The joint will just get re-irritated the next time you're active — cue another few weeks of painful knee cracking. While an over-the-counter anti-inflammatory medication can help reduce inflammation and pain, exercise is needed to help build stronger muscles so the knee is better supported.

"Whether it's long walks in the evening or a day at Disney, activity is necessary to enjoy life," Dr. Zalamea adds. "Strengthening the muscles that support proper function of the joint is critical for treating knee pain and making sure it doesn't come back."

Your doctor can help you understand what's causing your knee pain and the exercises needed to help relieve (and prevent) it. (Related: How to Get Rid of Knee Pain & When to See a Doctor)