If tightening the drivers doesn't work you will need to find the source of the buzzing. As mentioned above, it might even be something other than the speakers. The problem is that it only occurs when playing very loud. You can't be holding your ear next to a driver while it is producing 120 dB at close range. My recommendation is to buy a pair of Etymotic Research ER20 earplugs available on Amazon (and elsewhere). They are designed to reduce the sound level more uniformly across the frequency spectrum.
If you or anyone you know ever attends live amplified music shows these earplugs are absolutely wonderful. You can hear everything while saving your hearing. They also make great stocking stuffers!
When I had my recording studio I bought them in quantity directly from Etymotic. I gave them to the members of the bands I recorded (I did a lot of metal and hardcore) along with a lecture about preserving their hearing. The Etymotic guy asked what I was doing with them and when I told him he gave me an extra discount. Great people.