It's a bit hard to diagnose.
You may be able to replicate by having a companion listen to the motor whilst loading it up riding the clutch, but that's a bit dodgy.
I'd try investigating visually for a start, check the compressor wheel for ANY imperfections, they don't need much to sound awful.
Are you sure it's coming from the engine bay? the Isuzu's I've been in are that violent I don't know how you'd pinpoint the origin, if you can hear it really clearly, check it's not the line running to the boost gauge.
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