This transceiver with HM-56A (DTMF) pad immediately begins transmitting for 5 - 10 seconds when first turned on. Seems to happen when mic attached. Clicking the mic button has effect. This happens after set has been off for a few hrs or overnight. Rig is over 8 yrs old and has spent all its life in my car. Works OK, otherwise. Can anyone help? Is mic schematic available? -Larry W1DOY