You are not crazy. Iam also getting this in first person. I think it goes beyond being a sound bug. Iam fairly certain the movement animation is bugged as well and the sound in a symptom of it. There are at least 2 mods with bugs listed for this (Remington 870 Pump Action and RU 556). Neither of them list a solution. There is some speculation that lowered weapons or button lowered weapons is causing it but i cannot replicate that; seems to happen whether those mods are installed or not.