Box Resonence

I have a problem with a box I built for four audiobahn 10's.  It continues to resonate the box into creating its own sound.  Kind of a harsh grating sound when playing tracks with alot of midbass, and keeps me from turning it up to its full potential.  Box innards are braced and have tried polyfill, was wondering if maybe Dynamat or such applied to inside of enclosure would calm it down.  Any ideas would be appreciated.  Hope to have pics back in a day or two so all can see.  Thanks

If it don't fit, Force it.

If it breaks, needed a new one anyway!

Heres the pic of the box.  Any ideas will be tried and appreciated.  Thanks

Also it looks pretty huge for 4-10's.  Is it ported?  In general 3/4" MDF won't resonante to speak of, but it does need to be braced internally to prevent flexing.  I'd bet you need additional bracing, especially with a strange geometry like that.  Also, be very sure the enclosure is not flexing at all where the amp is mounted or you can very easily destroy the amp when it's mounted on a large wall like that.

Okay #1.  The amps are not rattling against the wood, they are mounted on rubber standoffs to eliminate that.

#2.  I used liquid nails for glue, and did both screw and nail the joints.  I prefer to screw all joints but because of geometry reasons some were nailed for added strength.  Carpet may not be an option, since the customer wants to finish with granite texture paint(you know the grey crap with black and white flecks?) But I considered carpeting the insides of the enclosure.

#3.  It is not as big as it actually looks, the box is only 13 inches front to back, and where you see the amp(s) it is actually sunk into the box clear to the front, and there is 3 amps in the hole.  One on each side, and the one you can see mounted against the back of the front wall...mind boggling description I think.  there are braces running front to back right above the amp space both horizontally and vertically at each side of amps. Also braces ran from rear point of diamond to front wall on each side.  Black lines indicate braces.

I appreciate everyone responding this quickly, I have been using this site for a while now, but never really did a lot of posting so Thank You all for the Ideas.

By the way, this thing sounds unbelievable except for the resonence, it can literally be heard from three city blocks away, a friend down the street at the convenience store called and told me to turn it down.