Did not tell this before. The Rub & Buzz sweep is pretty sensitive, it will indicate small vibrations and such.
If you recall the review of the purify speaker with the "distortion peak" 380 Hz, there is good chance of a enclosure or driver attachment vibration that caused it.
Attached below are two R&B plots: one with a 1mh choke sitting on top of the enclosure and the other plot without the choke coil sitting on top. Just a example of a enclosure vibration showing up on the test plot.
A Rub & Buzz plot is a recommended addition to speaker reviews.
Thanks DT