FPS drop

For the past few weeks, I've been noticing that my FPS drops suddenly at random times in game. And lately, the drop even sticks around. Whereas previously, I could consistently maintain 144 fps, it's dropping to around 100, sometimes less. and when the spike hit, it drops to less than 60. I haven't made any hardware changes or installed any new software. I've also research methods to increase fps and have done everything, nothing helps. hextech repair didn't do anything. Cleaning my machine, adjusting performance for max, adjusting in-game visual settings, etc. Nothing helps. At this point, I'm pretty stumped as to what the cause is.