... spin,

Units c=G=M=1 (M is the total mass of the Kerr black hole) and the Boyer-Lindquist (B-L) coordinates $(t,~r,~\theta,~\phi)$ are used hereafter.

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... oscillations

However, Middleton et al. (2006) refer to a substantially lower, intermediate value of black-hole spin, $a\sim 0.7$, to which the model of hump-induced oscillations cannot be applied.

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... orbit

We stress that the Aschenbach effect is frame-dependent, as it is related to LNRF, but recall the arguments for relevance of the LNRF point of view at the beginning of the section.

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... frequency

Combinational frequency $(\nu_{\rm r}-\nu_{\rm h})$ corresponds to the same order of nonlinearity as $(\nu_{\rm r}+\nu_{\rm h})$.
Note added in the manuscript: After the paper was accepted we obtained an information that a weak QPO at frequency 27 Hz is referenced in Belloni et al. (2001).

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... frequencies

p, q are integers.

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