  The crossing of temperature dependencies of sound velocity in the normal and
the superconducting state of metallic glasses indicates renormalization of the
intensity of sound interaction with two-level systems (TLS) caused by their
coupling with electrons. In this paper we have analyzed different approaches to
a quantitative description of renormalization using the results of
low-temperature ultrasonic investigation of ZrTiCuNiBe amorphous alloy. It is
shown that the adiabatic renormalization of the coherent tunneling amplitude
can explain only part of the whole effect observed in the experiment. There
exists another mechanism of renormalization affecting only nearly symmetric
TLS.
