How te heck do you get mud inside the radiator

. Anyway, I've pressure washed the radiator from the inside and outside a couple times so I'm thinkin thats not the problem. Just recently changed the coolant (mainly because the water pump bearings fried, siezed up and had to be replaced) and the coolant didn't look contaminated at all. How would I check the radiator for a blockage?
I have 2 lights mounted on the bumper. The passenger side one doesn't block any of the radiator "fins" and the drivers side only covers a small portion in the corner.
A while ago, the AC compressor sounded like it had marbles in it, only when the AC was on. I've had it disconected for a while now so not sure if it is still making that noise. Thats kinda why I was thinking it was the compressor or compresor clutch.
I'll also look into changing the T-stat.
Thanks for all the input,
DonC