When do you stifle mana drain?

[Thegreatgonzo]

I know that mana drain mana producing ability is a triggered, no mana ability, so it can be stifled. But when do you need to stifle? When manadrain is cast? When the trigger ability is on the stack (next main phase)?

I think the second option is the right one, because stifle targets the ability, not the spell, but could somebody confirm this please? Or prove me wrong?

Thanks for making this clear for me and my mates. (And sorry for the noobish question   )
 

[Shock Wave]

You Stifle the Mana Drain trigger that occurs on the next relevant main phase.

[The Atog Lord]

Does the Mana Drain ability use the stack? Or, like other abilities which add mana to your mana pool, is it considered a mana ability?

[Komatteru]

It is a triggered ability that adds mana, but that does not make it a mana ability.  In order for a triggered ability to be considered a mana ability (and not use the stack), it needs to trigger off another mana ability, and add mana itself.  Heartbeat of Spring's ability is a mana ability because it triggers when a land is tapped for mana, and adds mana itself.  Manabarbs, however, while triggered off a manability, does not add mana, and therefore uses the stack.  Carnival of Souls, which adds mana, uses the stack because it does not trigger from a mana ability.

[starfreakclone]

Well then since, or at least Im pretty sure, Lions Eye Diamond can only be played as an instant can its ability be countered?

[Komatteru]

No, LED is a mana ability with a specific timing restriction.  Any activated ability that adds mana is a mana ability, but a triggered ability may or may not be.

Rhystic Cave's ability can also only be played as an instant as well.