I purchased a Kohler Spa Tub from a contractor that had the tub stored in a warehouse. It was faded, but looked unused or mildly so.
I installed it with the side against a crawlspace on the third floor of my house. The crawlspace holds the air handler for the house and is up against an exterior wall.
A few months ago, I turned on the jets once the tub filled up and some debris came out of the jets. I picked it out to find it was a broken acorn and small bits. I chalked it up to being there from the warehouse storage.
Last night, my wife turned it on and more debris came out. Again, an acorn and small pieces.
I haven't hard any movement in the crawlspace (thinking squirrels). I assume that this thing has an air intake and that some rascal is placing these treats in that intake. I haven't seen any other signs of this though. No chewed insulation, etc.
Whirlpool tubs don't have air intakes from outside. They take air from inside the room.
Sounds like you got a rodent in there. somehow. I'd probably err on the side of caution when you think about filling the tub again...... If what you're saying is true, they've likely found their way under the tub deck and have chewed through the jet lines.