My son recently swichted from sax to euphonium in 6th grade band. The great part of the switch is the school loaned us the instrument for the year. On the down side I do not know what level of care the instrument received prior to its coming to live with us. This weekend the instrument started making a strange noise when certain notes are played, almost like something is flapping around inside so the note sounds inconsistent. Any thoughts about whether this is something easy to address or if the instrument needs professional repair attention? I am not inclined to attempt any repair on my own, but would like to know if continuing to play it while it is behaving this way will cause the instrument damage.