I would eliminate abs system from the equation by disabling it. Unplug the right fuse will do it else pull the connector on a wheel speed sensor.

It sounded very periodic at one point and that points toward CV joint. Are you just engine braking or actually hitting the brakes also?

At one point it also sounded like bad sway bar links but that's not periodic sounds more like Morse code.

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2011 E70 • N55 (me)
2012 E70 • N63 (wife)