my bank has no issues with coinbase. yes i use coinbase, since 2013. never had any issues at all. the amounts ive moved have surely caught the banks attention as any individual transfers over 10,000 USD get flagged. and i dont try to hide them (called layering? i forget. theres a term when avoiding hitting the 10k limit, like 9700, 8500 etc). so i do 10k on the dot chunks.
I never paid any attention to this.
If i needed 8k, that's what i withdrew; when needed 2k, withdrew that.
When I wanted a bigger chunk (a bit above 10k), then I did it too.
I can recall once being asked about it (by the bank) and since that withdrawal was for either mortgage or car, that was, indeed, my answer, not surprisingly.
Now, if we hit a serious value for btc like 100-200K/btc, then, I am afraid, even those who have a single digit corn for cashing out would have some 'splaining to do. In fact, regular checking is not even equipped to handle large cash loads inasmuch as FDIC insurance in US only covers first $250K. Investment banks might be a better destination, but don't take this as an advice. I have no idea if this is true (never tried).