They have a "clean" sound because of the tuning style particular to the band which only has a fifth added to the note (as opposed to a third, or a sixth)... somebody correct me if I am wrong.
This is not to say others' pans are noisy but rather that less complicated sets of frequencies transfer better within the limitations of digital audio replication...
Very true Noah
Those harmonics can can create much havoc on sound reinforcement and audio capturing for recordings if improper mics are used that cannot handle those partials at particularly higher volumes. In this regard, mic placement, mic type, players skill-set, instrument quality, tempo and tuners ability and recording sample rate all become serious factors in the "noise" quotation.