1992 w350 cummins grid heater problem
 

Hi I have a 1992 dodge Cummins the wait to start light comes on when engine is warm but when its cold the wait to start light doesn't come on and I can't hear the relays come on but after it starts the relays start knocking really loud until it is warm they knock loud enough you can hear it over the engine at idle wat could be the problem? Could it be bad relays?