We discuss two methods used for the study of unconventional superconductors: ultrasound attenuation and collective modes. These two methods, as well as microwave absorption, turn out to be coupled and have become very important now. Within models built by path integration technique we analyze some recent ideas concerning possible realization of the mixture of different d-wave states in high temperature superconductors (HTSC).We specifically consider the mixture of <img id="_x0000_i1026" src="../../../../img/revistas/bjp/v33n4/a02img01.gif" align=absbottom>and d xy states. We study the collective mode spectrum and the ultrasound attenuation in the mixed state, and show that each of the two methods allows us to distinguish a pure d-wave state from a mixed one. They also allow us to identify the type of pairing and order parameter in unconventional superconductors, including the presence and topology of gap nodes, the magnitude of the gap, and degree of admixture in the mixed state.