Hi,
My CI1 constantly causes hiss noise. Here is my setup:
Hiss noise produces whenever I start application requires CI1 to work such as iTunes, HALion Sonic, Cubase, Logic Pro…
Please help me on this.
Of course every piece of gear within an audio setup signal flow chain will produce a small amount of hiss.
To me it seems that you are reporting about a great amount of hiss that is not common and that all hell is breaking lose once the Ci1 activates.
Do you have any other equipment connected to the Ci1?
Could you please connect the Ci1 to other USB ports of your system? Interfering signals could be introduce through the USB connection to the iMac. If you hear the hiss through the headphone connection this would also be an indication for that.
The problem could also be related to the connection between the Ci2 interface and the HS50’s and interfering signals from the outside. Are you by ay chance using unbalanced 6,3 mm jack cables to connect between the Ci2 and the HS50’s?
If the jack only has a Tip and a Sleeve it is unbalanced:
A balanced jack should have Tip, Ring and a sleeve:
Could you try to connect the CI2 with a balanced jack or balanced Jack/XLR cable to the HS50’s?
Would it be possible to test the Ci2 on another system?
Is this hiss also produced there?
It would be really useful to know if the hiss also occurs on another system.
Gr,
JHP
I have the same problem with Steinberg CI2!!!
I get the noise with any vst effects in Cubase, FL Studio!
The more vst effects the more noise!
Noise depends directly on the CPU
Tested on several types of jacks
balanced and unbalanced.
My First System:
Windows 7 64 bit
Steinberg CI2 tested on My Second System:
Mac Pro with Mac OS version 10.6.5 in Logic 9
Intel Xeon 2,93 Ghz, 10 gb
The noise was but another character. Noise in CPU utilization as the PC - not confirmed
HELP ME! 
The more vst effects the more noise!
Seems like your experiencing ASIO crackles not noise.
In Cubase, are you sure that you have the “Yamaha Steinberg USB ASIO” driver selected under “Devices–> Device Setup–> VST Audiosystem”?
Select the “Yamaha Steinberg USB ASIO” driver under “Devices–> Device Setup–> VST Audiosystem”.
After selecting the correct driver beneath the point “VST Audiosystem” you will find the driver specific point “Yamaha Steinberg USB ASIO”. Click on this entry and then on the right side click on “Control Panel”. Set your ASIO Buffersize to 512 or 256 samples. If the problem returns in a big project in which you are using allot of VST’s, just increase the Buffersize to reduce the strain on the system.
Gr,
JHP
Hissing is not the Ci1. 
Gr,
JHP