High pitch alarm when ignition is turned on that won't stop.

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There is a deafening high pitch alarm that starts up when the ignition is turned on (even before the engine is started. It doesn't stop. This is a Winnebago Rialta that is based on the Eurovan chassis. The alarm appears to be coming from the dash area and not coming out of the speakers. I do not think the vehicle has an alarm system. It isn't the Carbon Monoxide or smoke detectors. The radio alarm (Panasonic) is disabled. Any ideas on what it could be? The local VW dealer refuses to look at it since it is a motorhome.