I have a 2007 Rav4 base model. Just recently the volume knob has been acting up. When I start turning the volume up, the sound actually fluctuates both up and down randomly. I can see the volume numbers both increasing and decreasing. Its almost like it's really touchy. I'm not sure if there is a simple or complex fix or if this is a common problem. I really don't want to replace the whole unit. Any help would be great. Thanks.