i'm now using z77x-ud3h with antec hcg-620m,
it does not have the problem that CHing you said...
have you tried running with other PSUs?
You may also switch on the ErP to see if the power consumption of your machine after S5 is high...so that it makes your PSU run in that way...
There are some power supplies still keep the fan on for 2 minutes after shutting down the PC for cooling down its component. Check the PSU manual and see if it has this feature.