Olivetti d-Copia 283MF Plus Operation Manual page 8

'CALL WAITING' or other telephone company optional services that produce audible tones or clicks on the line
can disrupt or cause termination of facsimile communications.
No matter what the status of the unit, if the sound of the motor within the unit is audible, never open either the
front cover or the left cover, nor turn off the main power switch.
vi OPERATION GUIDE