Knee pops when I squat

Just wondering if anyone can help me out with a strange knee issue. When I'm in the bottom position of a deep squat with heavy weight the inside of my knee will occasionally pop a few times. I'm not sure if it's something rubbing against something else or bubbles in my knee popping. It doesn't make the loud sound you get when cracking a joint. It's more of an awkward feeling that's not painful and I'll be able to get the weight back up. The next day though it gets sore. Any help will be much appreciated.