AM band crackle

Our 5's AM band crackles after the radio has been on for about 5-10 minutes. When this problem arises it happens on all channels and never varies or ends. FM has no problems. The noise exactly the same on all channels and it's pretty much intolerable.

The dealer is pushing back on it even though the car is still under warranty. Says it's a crackle that happens on other Mazdas, which is utter bull. If he pulls the radio and sends it out and nothing is wrong with it, he still has to pay for the "repair".

How do I pull the radio on my car? I want to see if I can find anything obvious although I believe AM radio uses an internal antenna. I also need something to look at to be sure they swap the radio when they say they did.
 
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