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.