I too got the h115i platinum from scan.co.uk. The Pump on its quiet settings does have an audible hum and is louder than the EVGA CLC 280 cooler that I had.
I also noticed the pump does not drop any lower than 2400rpm on quiet setting and goes up to 2800rpm on extreme setting. We could do with a 2000rpm or 1600rpm setting for quiet.
Because of the hum I might go for the dark rock pro TR4 edition air coooler, supposed to be decent?