Wouldn't worry too much about it, it sounds like it's just the tinkling sounds, different rates of contraction of the heatsink (alloy) that bolted to the chassis.
I have this amplifier and it does make noise when cooling. I never turn it off except for system changes. It sounds better when always left on. Putting in a Synergistic Research Blue fuse makes a nice improvement and is a one minute job.
Ever heard a house heating duct clang and bang mid winter when it’s belting out hot air and cooling. No different. Refractory lined cool systems are coming. Then again Class D is an efficient bulldozer. I can only afford late 90’s tech but it’s a pretty sweet ride.
I have called Pass about the noise on my amp and they said it is normal while warming up or cooling down to hear the clinking just the heat sinks contracting and expanding
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