So the initial roll-off below 18hz is 6db/octave based on what the manufacturer told me. The only thing we determined for a fact is that signals are being sent below 18hz at an amplification that is causing the spider coil to slam into something (believe he said cone) and that is what was causing the 'rattling'. He did go on to say it was something that would quickly damage the sub regardless if it was only a few seconds at a time if left unchecked. Disabling audyssey 'fixed' it for now. I don't know why anyone would let their sub get damaged once they started hearing what I was hearing....
As i said, when my part gets here (parts express had it on backorder) I'll update with my further experimenting. I miss the sound audyssey provides me in the mean time.
Mo, lets take a step back from the Audyssey argument for a second. First off, the cone will never actually slap the spider as they are connected together, rather it will hit the spider landing. and/or backplate. A few questions though:
1) Have you pulled the driver to look in the box and see if there is anything else that could be getting in the way and causing this tapping?
2) If you did, did you check the voicecoil leads and see if they might be tapping the cone on larger excursion passages?
3) If you haven't done these things I would strongly suggest trying this. I know it is some work, but sometimes box stuffing can even get between the driver's cone and the motor structure and cause issues. I have also had the VC leads get stretched before and cause tapping on several other drivers in previous setups.
If you do pull the driver, while it is out of the box, try tapping on the cone lightly and work your way all the way around the outside of the cone, tapping about every 3 inches and see if you hear any additional "tapping" coming from inside the driver. This could mean that the woofer is not seated correctly in the gap.
Just some additional things that you could possibly try out if you feel comfortable enough doing so. Beats just sitting on the sub worrying about it