help! my son is 7 and i'm freaked out

my son has autism adhd and tourette syndrome. we went to go visit my grandparents grave after school so while we there he told me i hear a man's voice and it's creepy. he said it's my papa voice idk how he knows that..then he said let's go please. we left and he said i don't hear it anymore he never hear voices until we went to the grave and that honestly creeped me the crap out man... he has never said anything about voices before until the grave... 😭😭