<human>: Can you provide a brief rundown of the text in within 3 sentences?

So, I have been doing so much walking over the past year or so, that apparently I can run 5k without too much trouble.

And since I have literally nothing else going on in my life, run I shall.

Question: After maybe 10-15 minutes of running, I am completely drenched in sweat, loving it, but when I move my head around it sounds like there is sand between the bones of my neck. Very fine grains of sand. It could also be described as the sound of poprocks.

I guess it could have something to do with my head, hair, ears, everything drenched in sweat.

My neck doesn't hurt. Gets kinda stiff when I run. I do the 5k in 28-30 minutes, depending on whether I get distracted by cats or free books, or not.
<bot>: Is it normal to hear poprocks inside your own head when running, and if so (or not), anyone know what that is / might be?