I have a customer using CRD5500-400CES  charging cradles for MC55A0-HC devices. We have an intermittent problem with multiple cradles where one or more of the MC55's emits a high pitched tone. It is relatively low in volume and I found it barely audible. but the setting is an emergency room and the staff finds it irritating. We have replaced the cradle, but no improvement.... I have asked the customer to replace the Power pack, but that seems like a long shot Has anyone else encountered this??? Any ides how to address it??