Sonomicrometer transducers that are not electrically isolated from the surrounding tissue fluids will typically pick up high frequency noise that will interfere with proper triggering on the received sound pulse.  RLMsono transducers are manufactured with a process that minimizes the chance that the transducer will be electrically leaky and they are individually tested to insure isolation. If you reuse the transducers you can retest them by soaking them in saline, and then measuring the resistance between the saline and each of the two leads.  The multimter should indicate an open loop; any measurable resistance indicates that the transducer is leaky and should not be used again.