The "rolling thunder" you might hear from within the building is rolling spheres between 6 - 16 lbs. hitting roughly 35 lbs. of wood covered in hard plastic at one time. Here's a video of where the sound is coming from: https://www.youtube.com/watch?v=41t76wh4uX4
Those with good geosense will make quick work of finding the container. Others might have to spend some more time working on it. Muggles shouldn't be a problem besides from the employees within that take a quick smoke break outdoors. Please return the cache container and especially the log as you found it so others may enjoy the search too.
Congrats to GingerMerican for the FTF!!