If the Mok'Nathal are tormented by the Bloodmaul ogres, then I will stop them and their followers. Ogres are simple creatures, and there is little profit they could gain from harassing the Mok'Nathal.
There must be something more to this. <name>, take Spirit, my hawk, and spy upon the conversations of the Bloodmaul's leaders. He may go undetected where we cannot.
Details
To find the ogres you are looking for, head down into the central ravine and head north pasts the Circle of Blood towards Gruul's Lair. The two ogres you are looking for are on the right side/east side of the ravine (location 58,30).
When you use the whistle, a ground target will appear. You will need to get relatively close enough to the ogres to use the whistle. You should still be outside of aggro range for those particular ones.
Reward
You will receive 3 70
Progress
What have you learned, <name>?
Completion
<Spirit perches upon Rexxar's shoulder, while Rexxar listens intently.>
So it is the sons of Gruul that are behind the ogres' actions. They command the Bloodmaul ogres to destroy the Mok'Nathal to gain their favor.