We studied high-bias conductance of Ag and Cu breaking nanocontacts and found that their transient conductance traces often exhibit a sudden conductance fluctuation and a subsequent rapid contact break, the same contact instability as we previously observed on Au nanocontacts [A. Fujii, et al., e-J. Surf. Sci. Nanotech. 2, 125 (2004)]. As in the case of Au, the conductance fluctuation tends to take place at a preferred threshold conductance G_th, which is found to increase in proportion to the contact current I. The slope of this straight I-G_th plot represents the critical current density j_c for the onset of the conductance fluctuation. Our experimental results show that I-G_th plots of Ag and Cu are nearly the same as that of Au, suggesting similar j_c values for three noble metal nanocontacts. [DOI:10.1380/ejssnt.2004.155]