My thoughts are if your vet friend only handled old military suppressors, then he is missing out on the vastly superior modern cans. I wouldn't call a suppressed .45 "virtually silent", but it's about as quiet as you're going to get outside of .22s because of their relatively low pressure and slow cycling. It won't totally muffle the combustion, and the cycling action on most of the firearms in that caliber (handguns) are still quite noisy. Carbines in .45 such as a suppressed AR variant will generally be even quieter.
I think the truth is somewhere in between on the scale of your argument.
So not silent
No, but about as quiet as you'll get with a decent caliber. Shockingly quiet even, but not silent.
I'm saying 90-100 decibels
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