When the log is growing, check the log_reuse_wait_desc for the msdb database in sys.databases. That should help narrow things down.

If it shows there's an active transaction, you should be able to figure out what the open transaction(s) is.

You can also check sys.dm_tran_database_transactions for the log_bytes_reserved and log_bytes_used columns to see what is actively writing to the logs.

For historical information, you can get some information by querying the default trace and looking at the autogrowth events for the msdb log. Something like the below should do the trick:

DECLARE @filename NVARCHAR(4000);

-- Current default trace

SELECT @filename = CAST(value AS NVARCHAR(4000))

FROM ::

FN_TRACE_GETINFO(DEFAULT)

WHERE traceid = 1

AND property = 2

-- Preserve the path and replace the current default trace with log.trc

SET @filename = LEFT(@filename,

LEN(@filename) - CHARINDEX('\',REVERSE(@filename)))

+ '\log.trc'

-- Auto shrink/growth events in the current trace file

SELECT TE.name AS [EventName],T.DatabaseName, t.DatabaseID, t.NTDomainName, t.ApplicationName, t.LoginName, t.SPID, t.Duration, t.StartTime, t.EndTime, t.textdata

FROM sys.fn_trace_gettable ( @filename, DEFAULT) T

JOIN sys.trace_events TE ON T.EventClass = TE.trace_event_id

WHERE TE.name like '%grow%'

ORDER BY t.StartTime;

Cheers!