I have one tail rattler right now (Una) and she only does it while she's eating.
Open the tub, nothing.
Pick her up, nothing.
Put her in the deli, nothing.
Drop a mouse in the deli, bzzzzzzzzzzzzzzzzzzzzzzzzzt!
And then it's nothing but bzzzzzzzzzzzzzzzzzzzzzzzzzt! until the mouse is gone, at which point, she's perfectly quiet again as I put her back in her tub. :shrugs: She's goofy like that.
I realize that's not very helpful, but really, you've already gotten the best advice from those who have posted before me.
It's a "nervous" behavior, not an "aggressive" one. It just takes time for your snake to get familiar with you.