I have a 2005 Toyota Matrix. The radio volume control knob does not change the volume. The volume is just constantly stuck at a set volume (luckily a reasonably soft one). I pulled the knob plastic cap off and sprayed some contact cleaner in there but nothing changed. Any ideas what caused this problem and what I can try? I have taken the radio out and opened it (changed led bulbs) before so I feel comfortable doing that and tinkering around.