In my experience, bard hate has nothing to do with faction. Here's what
happens. Puller grabs a MOB, usually by whacking on it, or shooting it with
an arrow/spell. This MOB is then very angry at puller for having done
damage to it - great! exactly what we want. Everyone then assists the
puller and continues to whack on this MOB, keeping its attention mainly off
the bard.
Here's the problem. The MOB that is being pulled seldom comes alone, he
brings along all his closest "friends". These "friends" haven't been
whacked, so their hate level is relatively low towards the puller, in fact
this hate level is next to none. Everyone is busy whacking on the original
pulled MOB, so these "friends" don't have any increasing hate level to
anyone in particular because nobody is hitting them, they just came along to
lend a hand. When it comes time for these "friends" to chose a target, they
naturally focus their attention on the bard since nobody else is really
doing them any harm, but a bard healing/buffing is considered to be dealing
damage to the "friends" themselves as far as hate is concerned.
The result - one MOB attacking the puller/tanks/casters, the other 5 or 6
MOBS focus on the bard.

How to cut down on this behavior:

1) Don't start playing songs before the fight begins. when MOBS first
arrive, their hate level is at its lowest, and they will go directly for
you. Sometimes even the pulled one will jump you as your healing outweighs
the damage done by the puller.

2) If their are more than 2 MOBS, don't buff/heal your entire party, unless
you have a tank that knows to taunt the extra MOBS off of you. Generally, I
don't play buff songs if there are more than 2 MOBS. Two or more monsters
focusing their attacks on the bard mean the healer has to concentrate solely
on you, when the tanks could have been absorbing the damage much better.
I'll concentrate on charm

3) The healing song is one of the largest taunts. Be very careful using
this in multi MOB situations, it can easily mean your death.

Elwyn Heartstring
Level 41 Bard
Erollisi Marr

<snip>
The possible answer to this is faction. If the extra mob hate for bards
is done intentionally by Verant, it's possible they base it on faction.
As it's been noted the Avaiks have no faction it's also possible they
haven't been programmed to hate any factions either. I would say if you
took away the magic thing that makes bards and bard songs the top hated
thing by mobs you would probably rarely end up at the top of their hate
list by your own efforts, as you would rarely if ever do more damage
than anyone else in your party. Even the benefits of the heal song would
be quickly eclipsed by the first heal cast by a cleric/druid/shaman of
your level.
<snip>