Rattling noise within laptop while typing or shaking
I am on my third rMBP (first had a defective battery, second had a defective hinge). After a few days usage, I am noticing that a large item inside of the laptop is loose. It can be heard when typing, and seems to knock on the bottom cover when the laptop is closed and shaken. I took it to the Apple Store today, and shook it in front of the "genius". He told me he couldn't hear it or feel it, and took it in the back room and had "15 people try to hear it" as well, but none of them could. He reports opening it and seeing nothing wrong. When he handed it back to me, there was no rattle.
Sure enough, I'm home and I'm using it once again and the rattling has begun. When I close it and shake it, I can hear it knocking around inside. What's strange is that as I let the laptop cool down, the rattling minimizes or goes away.
Is there a chance that the battery glue is weak on this particular unit and is coming loose when the laptop is hot? If so, what should I do? The Apple Store geniuses are consistently unhelpful when I visit the store.
Edit: I might also add that the object seems LARGE, like what I believe to be the battery cells or a board within the unit. I've worked on laptops for 15 years and this is the first laptop I'm literally locked out of (pentalobe screwdriver on the way). Just wanted to do some research in the meantime. Not sure what to expect when I open this thing.