how about this as a working proposition:
rhythm is not a thing, not a form, not even a pattern, but a sense ?
(thus, a special case of temporality, which is the sense of dynamic, change, …)
rhythm is not sonic
rhythmic is not unidimensional
rhythm is not metrically regular, or metric at all.
after Goldsmiths talk: Rhythm and Textural Temporality: An Approach to Experience Without a Subject and Duration as an Effect