Handymann - much appreciated and relevant. I did a lot of platform and feet mods with my Vpi Hw19 to good effect but mods have so far little effect on the Hanss t30 with its maglev feet. And - my vinyl recordings are made with the main speakers silent or very subdued. So I doubt acoustic feedback is the main culprit in this case.
The woofers on the Aurums are smaller but the behavior is similar to the Audiokinesis woofers. Some sound related vibrations but also pumping in and out. Yet I dont hear this movement at least not directly. Using my fingertips there is energic quick vibration that I hear but also a slower pumping that i dont hear.
Listening more, the experimental nature of Echoes and the whole Meddle album shines through. In other words it may well be that they experimented also in the low frequency range. They used Shepard tones and invented seagull squeals, I read. It is one "flowing" album and the silences between the tracks are not just silence but e g wind blowing too like at the start.So it is maybe a quite special case.