I often drive the 535 with the radio off.Sitting at the traffic lights the other day i could hear a light thumping sound aprrox two seconds apart.Stopped in the garage and turned car off,then turned key back to pos I and opened bonnet.Quickly traced sound to the heater vavle area.
The top of the heater valves were hot and could feel and hear them opening and closing???Or is it the pump???
Any thoughts gentlemen???