My Nuvi 350 speaker was broken and intermittent.
I followed the disassembly instructions here and here and replaced it with a Kobitone 254-PS606-RO Mylar Speaker which I ordered from Mouser Electronics for US $1.48.
There is some discussion at Fixya.com Instructions Replacing Nuvi speaker and Speaker Garmin Nuvi 660 Doesn't Work which claim the Nuvi 660 is the same speaker, but they give no details on what the part is.
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