Verify Game Files
Clutching at straws here, but have you tried 'Verifying Integrity of Game Cache'? Not sure if this will help but worth a shot:
Steam article on how to do this:
Found this on a reddit thread:
This is most likely your computer loading textures on the fly. There
is a config option to force preload all textures instead of loading on
the fly, cl_forcepreload 1. Try adding that to your config or just
enter it into the console.
Another Possible Fix
If you open net_graph you will probably see a lot of choke the moment an enemy
gets close to you. Try to use the command 'rate 80000' if your playing
mm and if you play on 128 tick use 'rate 128000' and see if that
resolves the issue.
You may have to enter this command every time you play but at least at makes the game playable.
I know it sounds strange but the game may be having trouble loading the sounds in game, ensure that your sound drivers are all up to date
If you are running any external software that affects sound or maybe software that captures gameplay, try playing the game without it and see if that helps.
This seems like an issue that will pop up for people for hundreds of different reason so my advice, if none of these work, is to just take a look around at different forums and articles, try all of the different fixes and hope for the best.
Hope I helped, good luck.