The best ways I've found to discover never heard before details on a recording is to either get a new piece of equipment, and listen intently, or to have someone point out minutia that they've heard when also doing intense listening.
So in a room of people you say, "wow, now I can hear the squeaking kick drum pedal," just as you first notice it, and everyone else will go, "oh, wow, I do too, that's amazing."
I can't say for sure what you've heard before, and the listening conditions. But this is why true double-blind testing is needed. Once you hear a new detail on one piece of equipment, you must be able to quickly switch to the other, and see if you can hear the same thing, and then back again. But you can't know which you're testing at any point.
