ACARS is purely text-based and has no voice mode. Something got lost in the description. ACARS could have malfunctioned because the radio frequency it uses was occupied by a voice signal, but I doubt that the pilots would be able to state the cause of the malfunction so quickly.

Remember "A mysterious voice is haunting American Airlines’ in-flight announcements (waxy.org)"?

Now it's the ACARS system, in Europe.

«A Sun Express Boeing 737-800, registration TC-SEK performing flight XQ-997 from Munich (Germany) to Izmir (Turkey), was climbing out of Munich's runway 26L when the crew requested to level off at FL100 reporting they had an unusual voice on their ACARS. The crew subsequently decided to return to Munich where the aircraft landed safely on runway 26L about 30 minutes after departure.»