High utilization by java

I installed a new Zimbra server (Release 8.0.3.GA.5664.UBUNTU12.64 UBUNTU12_64 FOSS edition) in a good server (Xeon / 16Gb RAM / hd sas).
But without users access (out of production) , the CPU utilization reaches the maximum, with IDLE=0%, and the java processes are eating all the cpu utilization.

Java process:
31813 ? Sl 24:53 /opt/zimbra/java/bin/java -client -Xmx256m -Djava.net.preferIPv4Stack=true -Dzimbra.home=/opt/zimbra -Djava.library.path=/opt/zimbra/lib -Djava.ext.dirs=/opt/zimbra/java/jre/lib/ext:/opt/zimbra/lib/jars:/opt/zimbra/lib/ext-common:/opt/zimbra/lib/ext/clamscanner -Djava.io.tmpdir=/opt/zimbra/data/tmp -Dpython.cachedir=/opt/zimbra/data/tmp/jython-cachedir org.python.util.jython /opt/zimbra/libexec/zmconfigd

Java version:
java version "1.7.0_15"
Java(TM) SE Runtime Environment (build 1.7.0_15-b03)
Java HotSpot(TM) 64-Bit Server VM (build 23.7-b01, mixed mode)

Thanks for any help !

Alessandro