It's a problem with your routing but I also think you've stumbled upon the limitations of USB mixers. Jeps! Help me out here!
@KitC
juuujooong!!! im here sensei!
@demet
Like what my SENSEI Master KitC posted in different threads before USB is somewhat limited unlike the firewire versions. USB is is 50% slowers on the transfer rates.
actually pretty much covered lahat ng sinabi ng Master KitC ko.
Im gonna share a tru to life story.... hehehe
I Use to have a PC that doesnt have a USB 2.0 port and i get the same problem as yours using my USB Mixer. When i upgraded my PC and used the 2.0 port all the noises was "reduced" not totally gone. Thats the time i decided to go firewire. When the guy who bought my mixer is already using the mixer iwas really surprised why he aint getting that problem (without him knowing what im looking for and without him knowing why ireally sold that to him). I Checked his settings (chain, mics, adn applications) and found nothing special about it. When i checked at the back i saw that he used a different USB cable (brand New) and he said he had to buy a new one coz the one i gave it to him is causing hums and grounding. I said to myself it doesnt really make sense coz a USB cable is only transfering data to pc.... NOTHING MORE.
Then after a month he gave me a call and he said he's getting those noises. I told him to call Alesis about it and what the support told him is to use the application budled with the mixer, check any groundings in the PC, Check if the PSU is regulated....
He then bouaght himself an HEC PSU.
AND WALAH!!! no more problem!
a silly story pero thats what really happened
hehe