Did you checked scheduled Maintenance Tasks in your environment?
You can check out the tasks status by this SQL query:
select *, floor(DATEDIFF(ss,laststarttime,lastcompletiontime)/3600) as Hours, floor(DATEDIFF(ss,laststarttime,lastcompletiontime)/60)- floor(DATEDIFF(ss,laststarttime,lastcompletiontime)/3600)*60 as Minutes, floor(DATEDIFF(ss,laststarttime,lastcompletiontime))- floor(DATEDIFF(ss,laststarttime,lastcompletiontime)/60)*60 as TotalSeconds from SQLTaskStatus