Iron inductors seem like a no-no. In fact, I got huge coherency improvements by taking anti-static and EMI measures on it with some usual hi-fi tweak products. I do not know if they even tried to orient it correctly.
Sounds like you identified it to me 😁
Iron core inductors work just fine, in fact often better because their DC Resistance (DCR) is lower since they don't have to have nearly as much wire involved to reach a certain inductance value.