Slow waves generated by ion cyclotron instabilities in tandem-mirror end cells may propagate into the central cell where the waves may degrade ion confinement. Such propagation and degradation occurred in TMX, but not in TMX-U because of the improved neutral-beam injection geometry of the latter device. Fast waves observed in a central cell may arise by mode conversion near the ends of the central cell if the slow-wave amplitude is large there and if the slow and fast waves have comparable perpendicular wavelengths. Comparable wavelengths were present in TMX, but not in TMX-U; the fast-wave amplitudes observed in TMX-U which are much lower than those in TMX are thus consistent with mode-conversion theory.