My Jetta makes a beeping/ringing noise sometimes. Usually at highway speeds, sometimes when starting from a stop, and only while my foot is on the gas. Around 1700-2000 RPMs. It stops the second I take my foot off the pedal. It sounds like it's coming from the passenger side of the dash. It happens even with the radio system powered off, and AC off. The dealership spent three weeks trying to figure it out, but couldn't. Any ideas?