I'm trying to manage the aggro so I can take the goblin camp one surgical strike at a time. I've had some success in other situations where I use crates, etc. to climb on or block things off, except for the goblin war drums. I've tried piling stuff on them and around them, but nothing seems to block the goblins from getting to them. How are gobbos still alerting the horde when I've covered their drums in a mountain of junk?

Just start the fight by destroying the drum

Well, that worked. Funny, it never used to let me target the drums.