This perhaps explains why I haven't experienced any buzzing on my speakers. I only use banana plugs on the amp side due to hassles getting the amp in and out, but have screwed down the ends on the speaker side.
Some of those banana clips do have loose, rattly parts, and I'm sure the Monoprice ones, in particular, where the screw-on parts (handles?) can easily work loose, are probably major culprits. Other banana clips have the connector part in two pieces (one rotates inside the other) and may also tend to rattle.
It would be interesting to see if any others, who hopefully still have their ELACs, have tried removing the banana plugs from the speaker side and screw the wires directly into the connectors, and then retest.
Also, I need to add one more digit to my serial number report. My speakers are
31970E004xxx, right in the range of the others reported here, earlier than the other two I read.
Mine are mounted on wall mounts (
https://www.amazon.com/VideoSecu-Clamping-Bookshelf-Surrounding-MS56B/dp/B000X9O8SI), screwed directly into wood studs, and securely clamped with the rubber pads provided. They sound great, even though I almost screwed one up by pushing on the tweeter chasing distortion that was actually coming from an amp with too much DSP artifacts.
I would imagine rattly banana plugs are a good way to expose cabinet resonances in any speaker, but that probably also depends on the resonance of the particular banana plugs.
So, maybe if you report which plugs you used (if you used plugs), we can see if this is a valid pattern, and if there is one brand that rattles with these more than others.
It seems cabinet resonance is the issue, particularly in the back.
Dan