I'm not sure if this will help, but I experienced a similar crackling sound and it was a cable shield that wasn't earthed. Once it reached a certain level it discharged across the inner insulation.
It was a quality brand subwoofer cable with terrific shielding. Problem was it wasn't earthed. After slicing back a slither of the outer protection I gently soldered a wire to the shielding and connected it back to a central earthing point. Fixed.
Unidentifiable popping sound
Not 100% sure it goes in this forum — apologies if there is a better place.
For 6 months now, something in my system is making a clicking/popping sound. It usually happens 15 minutes after I power things up, or about 10 minutes after I power them down. It can also happen spontaneously when everything is technically on standby. I actually have a recording of it, but not sure how to upload here. Any ideas?
Preamp — Nagra Jazz (possible) (it happened with both old and brand new tubes)
Amp — Nagra Classic Amp (possible)
DAC/Source — PS Audio Directstream (possible)
Phono stage — Pure Audio LV-1 (probably not)
TT — Clearaudio Concept (definitely not that)
Cables — Luna Orange (also, definitely not that)