Seismic scream precedes volcanic eruptions

The transcript describes the events leading up to a 2009 volcanic eruption. It details a series of tremors occurring two kilometers below the crater, which escalated into a swarm of 1,600 drumbeat earthquakes in the 10 hours before the eruption. The frequency and occurrence of these tremors increased, culminating in a continuous scream that peaked 30 seconds before the eruption.

What event occurred prior to the 2009 eruption?

How deep were the tremors recorded below the crater?

How many drumbeat earthquakes were part of the swarm before the first explosion?

What happened to the frequency of the tremors as the eruption approached?

What was the nature of the noise just before the eruption?