The aura is visually distracting and the fact it can remain up indefinitely while people are AFK out of combat means it's a very common, very obvious, very persistent distraction.

I almost hate to use it in dungeons myself for the same reason. Either let it be affected by combat effects settings, switch it out, or disable it until the new one is ready. PLEASE. (And to those that wonder how a DRK will remember if it's active if there is no visual effects, please go look at other tank jobs.)