I agree with fhw.
If you can actually isolate the noise to one woofer and it occurs with more than one dvd, which by your experience it seems to have done just that, then have Joe send you a new woofer.
If you want to test it another way yourself, swap the position of the buzz woofer for another woofer in the vp150, play the dvd again, and see if the same woofer still makes the buzz.

"Those who preach the myths of audio are ignorant of truth."