What Triggers sp_recompile in database without triggers, stored procedures, etc?
The SQL Server engine doesn't explicitly call sp_recompile in order to remove plans from the cache.  As far as I know anyway.  There might be features of SQL Server that do this, but I haven't heard of it.

The mostly likely culprit is that some individual or user process is calling sp_recompile.  Hopefully you can tune the tracing process you mentioned to capture the user executing this call.

I recently noticed that calling this on a table or view takes a SCH-M lock on that table or view, which would explain the blocking (no reads or writes can take place against the table with this lock in place).  It does not take very long on the systems I have access to, so I'm not sure why it would cause blocking for a long time.