I have this issue as well.
On my gen 1 air pod pro's (now my wife's very nice hand me downs) when I put them in with noise cancelling on, it feels and sounds like I am in a sensory deprivation chamber, until whatever I am listening too comes on.
With my air pod pro 2s, that feeling is just gone and there is now a white noise or very low but super noticeable hiss, as described from so many others (and growing as times goes on) around the web.
I just picked these up and have 45 day return on these due to the store/card policy I got them from, so if no update from Apple that addresses this in the next 40 days, I will return, recoup $50 and grab a new pair of gen 1's on sale.
It's too bad other than this weird ANC hiss, I like the gen 2's and find them generally a true upgrade. They sound better overall, they last a bit longer battery wise, the upgraded case features are cool, the adaptive trasnparency is legit (although I won't use it much if ever), and the big one for me was having on stem volume control.
BUT this hissing sound bothers me enough to give it all back for the true quiet feeling I get from gen 1's. Knowing Apple's response time to fix issues (or even acknowledge there are issues) these days, I reckon that is exactly what I'll have to do.
