Bangs when shuts off

I have a Frigidaire (freezer Up), probably about 10 years old. We have
been noticing an increasingly louder clunk/rattle when the compressor shuts
off. It does not seem to be off the rubber grommets the compressor rests
on....it seems to be something internal in the compressor that is loose and
rattles/clunks loudly when it shuts off. It is still cooling properly but I
am becoming concerned.

What you describe is what we call in the trade "shutter stop". This is an
internal problem inside the compressor itself most common to "Embraco" brand
compressors manufactured in Brazil. Although, I have seen this lately in
Techumse compressors that have recently started to come from Brazil.
Techumse was previously a stateside brand. (Viva la free trade!)

Sorry to give you the bad news but the only way to get rid of the noise is
by replacing the compressor.

How long will it live despite the noise?

That varies, I've seen some go down as early as 6 weeks after it began, and
others have gone on for years.