Why do I see sp_OACreate, sp_OASetProperty in sp_WhoIsActive?
Did you search your system catalogs for stored procedures that might be calling them? In DBs where you see this:

SELECT OBJECT_NAME([object_id]), definition
   FROM sys.sql_modules
   WHERE definition LIKE '%sp[_]OA%';


To do this for all databases at once:

DECLARE @sql NVARCHAR(MAX) = N'';

SELECT @sql += CHAR(13) + CHAR(10) 
   + 'SELECT ''' + name + ''', o.name, m.definition
   FROM ' + QUOTENAME(name) + '.sys.objects AS o
   INNER JOIN ' + QUOTENAME(name) + '.sys.sql_modules AS m
   ON o.[object_id] = m.[object_id]
   WHERE m.definition LIKE ''%sp[_]OA%'';'
FROM sys.databases;

EXEC sp_executesql @sql;


You might also check job steps.

SELECT j.name, s.step_name, command
   FROM msdb.dbo.sysjobsteps AS s
   INNER JOIN msdb.dbo.sysjobs AS j
   ON s.job_id = j.job_id
   WHERE s.command LIKE '%sp_OA%';


If you don't find anything there, you will want to run a server-side trace because it must be coming from ad hoc batches.