I am using an IC-r75 and I was listing to some utility stations today and notced that there was some interference that would spike from s1 to almost s5 on my meter. It would happen about once per second and it made it almost impossible for me to set my squelch level. I tried turning off all of the noise sources I could think of and that made no difference at all. However, when I set the AGC control to "off" the noise stopped. I also haven't heard any traffic on the station I was listening to either. What is the AGC used for and should it be turned off when listening to USB? I bought this receiver used and it didn't come with a manual so I'm a little lost here. Any help would be appreciated.