Cron job has started producing output
Not sure why it's suddenly started producing output when it didn't previously, but you could use:

#!/bin/sh
a=`drush -r /home/crwheelmen/www/www --quiet civicrm-api job.execute`
if echo $a | grep -qv '\[is_error\] =&gt; 0'; then echo $a; fi


(capture the output of drush to variable a then check whether is_error is 0.  If it is, do nothing otherwise show the output)