Can you feel the trailer move a little, or sort of lurch a bit or something when this happens?
I would suspect something in the suspension, such as a shackle that is perhaps bound up a bit and it suddenly moves as the trailer sits a bit after being set up, and it settles from movement inside.
Or perhaps a spring itself?
The sound of a shackle settling / moving would echo loudly through the spring, giving a metallic sound as you describe.
2007 GMC 3500 dually ext. cab 4X4 LBZ Dmax/Allison - 2007 Pacific Coachworks Tango 306RLSS
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