Slow query

Please help me speed up the following query. It used to run in 2-5 sec.,
but now it takes 2-3 mins!
I ran VACUUM FULL ANALYZE and REINDEX.
SELECT * FROM media m
WHERE m.mediatype = (SELECT objectid FROM mediatype WHERE
medianame='Audio')
AND EXISTS
(SELECT * FROM
(SELECT objectid AS mediaid
FROM media
WHERE activity='347667'
UNION
SELECT ism.media AS mediaid
FROM intsetmedia ism, set s
WHERE ism.set = s.objectid
AND s.activity='347667' ) AS a1
WHERE a1.mediaid = m.objectid
LIMIT 1)
ORDER BY medianame ASC, status DESC

Basically it tries to find all Audios that are either explicitly
attached to the given activity, or attached to the given activity via a
many-to-many relationship intsetmedia which links records in table
Interaction, Set, and Media.
I attached the output of EXPLAIN and schemas and indexes on the tables
involved. Most of the fields are not relevant to the query, but I listed
them anyways. I discarded trigger information, though.
Thanks for your help.

Oleg

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