Actually, some of Corsair's PSU's are still made by Seasonic, for example the
AX760. Interestingly, the AX760
i is made by Flextronics.
As for the OP's problem, I know it sucks, but what exactly do you expect Tt to
do about it? As long as the PSU is running as per their specifications, they're
not really obligated to do anything. If the PSU is simply a loud PSU
by nature,
according to them everything is ok. You're simply a customer who is not
satisfied with the product he bought, but the product itself is actually doing
exactly what it's supposed to do.
I'm not saying it wouldn't be nice if they helped, but technically speaking,
nothing has actually gone wrong (again, provided the PSU is not broken).
EDIT: I'm not sure about consumer protection laws where you live, but here
you can return the product for a refund up until a certain time after buying it
if you're not satisfied. Not sure if that's an option for you though.