I did hear of an incident of someone losing 15,000 dollars and every car was searched and people were questioned until the money was found. By the time the cleaners get the car has been strip searched by budget employees.
Its gone forever. I left a bag behind on accident and they told me the car was cleaned and passed onto the next renter.
Give them a call and go back to parking lot and see if your speaker is on the ground some where.
They have a lost and found window. I would call them
I recommend contacting the rental company immediately and waking them if anyone found anything closer to their cars. It's a long shot but needed anyway.
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