A few thoughts:
1. Have you checked the screws that hold the driver in place? I've found that over time they can come a little loose which allows the driver to rattle under certain circumstances. I check mine roughly every 6 months and in most cases, some require just a smidge (an engineering term) of a tweak to tighten. If you do this, don't overtighten - they just need to be snug.
2. Can you describe your calibration process in more detail? Did you just set the speaker levels (and how did you set the sub relative to the other speakers) or did you also use sine tones and check the room for response over the lower frequencies? What calibration disk did you use for speaker levels - or did you use the test tones from your receiver/pre-pro?
3. Ever heard port noise? Looks like the port for the EPs is right under the driver so it may be you're getting some chuffing and confusing that with driver noise. At roughtly what SPL relative to reference are you hearing the noise?
BTW - does anyone know what the native tune point of the EP500/EP600 is? A quick scan of the manual didn't disclose it. Also has anyone seen any writeup of the behavior of the DSP in the 500/600 - e.g. what it does and when?
Cheers,
Doug
