There is a tapping/clicking noise when the engine is running. on 1998 Volvo S90

The radiator indicator light remained on for a very short time after I started the car. I opened the hood and the radiator cap is missing.

Asked by for the 1998 Volvo S90
repl cap and the seek insp of other issues
1 more answer
replace cap, ensure that you replace any loss antifreeze, in radiator, and resovior bottle. may need to get air out of the system by bleeding system. If tapping continues seek shop help to determine the cause of the tapping/clicking. Also the vehicle may have set a code, may need diagnostic scan.