First off, I admit I have been tinkering with my receiver settings lately. However, I may have been noticing this for a while before but was blaming the wooden shelf not far from it. Hard to know for sure now.

I'm calling it a rattle for lack of a better term. At first it sounded wooden, as above. However, it grew bad enough I brought my head over in front of the driver and it seems to be produced by the driver. When you are close and looking at the driver, it gives you the feeling that the rubber diaphragm is making a vibrating, flapping noise. However, this could be an illusion, influenced by the fact that I am watching this big rubber ring vibrate mercilessly in and out.

It occurs in the very low LF effects in movies and very deep bass drums in certain music. Increased volume definitely increases it's presence but it is also present in really low LFE at very moderate volume levels. As long as there is that prominent LF that it has to work hard on doing the lows, its there.

Chance of abuse as the cause is honestly minimal. I'm not a screamin loud kind of guy. Even for movies where I really want to stress effects, it's usually 75 to 80 db averages and some spikes into the nineties. If someone really wants to hear a loud demo, I'll give them the volume control but I shut them down if the peaks are breaking low triple digits. (I always take out the meter during demos so I have that exuse plus...I'm a geek. :-) I don't think I ever gave the sub more than it could handle. Maybe when I first tested it out but even then Im sure it can handle more than my ears can.

EP500 is running off a Denon 3608. I confirmed that these settings are back where they normally are.

- Denon's set for zero DB adjustment on the sub. All other speakers calibrated to equal levels.
- Sub distance is set to 13' (have tried larger numbers and I almost think it helps mask the rattle so I left it at 24' but its normally 13)
- Set for LFE, vs. LFE & Main

- Sub 'rattles' worst when set to full. Currently set to Flat where there is less rattle.
- Dial on the sub has always been at around the 9:00 position. I'll play with it a bit depending on seating but that's the norm. 9 o'clock gives me decent bass in my sweet spot but is too much in the corners of the room. (Square, hard room)

I can see no visible damage to the outside of the driver, I have put pressure on areas like the port and sides to see if it is something vibrating there but it honestly doesn't sound like a box vibration. Gives the impression it's in or around the driver materials.

Another symptom I noticed is that when I try to check the DB calibration and play a test tone with Avia CD, the meter wavers up and down by up by a variable of up to 5 db plus or minus. It's digital so it's hard to tell if its an even, 'sine wave like', up and down but I would think I should get a more solid reading.
Note: The sub tones on Avia are set up to play alternating against the other speakers but it is just during the sub tone that I am still not getting a solid reading. Perhaps this is normal?

Sorry too much info probably but I'm hoping the hard core readers will have some advice as to what I might check on. I'm open to further probing questions if you think you can help.

I'd like to rule out that I didn't make some other change to my setup or at least get the advice from the experts here before I start down the path of deducing my sub may be having issues.

Thanks all!

With great power comes Awesome irresponsibility.