We have a 2004 Dodge Sprinter 2500 Van 5 Cylinder Mercedes Turbo Diesel. Recently, at around 70,000 miles, when we start the engine block heater, the sounds are not normal. The heater appears to start working, since we can hear and smell the burner, but the heating ceases within a few minutes. The unusual sounds continue until the heater is turned off. Can anyone help with this?