So the other night, I was doing some work on my late-2013 13" rMBP in the den and when I went to rest my hands on it to begin typing, I heard a weird crackling-like noise. I thought maybe something was caught underneath it, between the bottom and the table, but nope. Upon further inspection, it seems that one of the black pads on the bottom has flattened out. It's almost like its 'depressed," like a button and moves a little. I got curious and pushed on the 3 others, and one of the other ones made a crackling noise and depressed in too! Has anyone ever experienced this? Should I be worried about them falling out or anything? I am not too worried because I know this thing is getting a little old now, but just curious more than anything. TL;DRL my 2013 rMBP is losing its feet.