Recently I've been hearing a metallic buzzing or rattling sound 1.3k - 1.6k as I'm slowly accelerating. It sounds like metal on metal and it sounds like it's coming from around the firewall area on the passenger side. Definitely sounds more like an engine bay noise than an in cabin noise. Truck is driving perfectly fine otherwise and nothing looks out of place or damaged upon a quick visual inspection. While I'm not 100% sure yet, I feel like it's only happening when the engine is cold.
It's about 5.5 years old, has 86k miles and the only mod is Bilstien 5100's all around.