We had a discussion a couple months back, it is at the link below.

I finally got around to removing the offending driver, and I'm not 100% sure it is blown. With the driver out, I can make it make the buzzing type noise by covering the little screened port at the back of the driver. Is that normal for it to buzz when the port is covered? If not, then does that mean it is blown?

Fresno

• http://www.audioroundtable.com/PiSpeakers/messages/15087.html

I still think the speaker is blown. It sounds like the voice coil is rubbing. If the voice coil is overheated, it will deform and begin to rub. Sometimes I find that speakers with rubbing voice coils buzz unless some pressure is put on the cone, other times, they buzz more when pressure is placed on the cone. I think that's what is happening to you - The slight backpressure from plugging the cooling vent exacerbates the problem. If you'd like, I can send it to Eminence and see if they'll warranty it.