Topic: maximum USB wire length

just a question for beginners , i just received my UFX II plugged on iMac Late 2011 , i use à +-5 meters USB câble and sometime some strange noises appears during recording on Logic Pro 10.3.2 (buffer size 128).not often but sometimes
Don't find also the Fx return , may be Avid CoreAudio.plugin and HAL  problem , i will see that later .
otherwise all is Ok