1)
Why does it mention that the Pelishtim heard the Teru;os?
1.
Malbim: (a) Even though they were far away, they heard it
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. (b) This caused them to investigate the reason; they learned that the Aron came.
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I.e. they blew very loud. (PF) Metzudas David learns this from "va'Tehom ha'Aretz."