A clicking noise may be noted from the turn signal flasher after the turn signals are switched off. This is commonly cause by a faulty turn signal switch which will require replacement.
Car Problem Reports
GMC Sierra 1500 HD Turn Signal Switch May Fail and Cause Clicking Noise
GMC Sierra 1500 HD Problem
Average Mileage: 177,333 mi (114,000 mi - 235,000 mi)
Visitor, 2004 GMC Sierra 1500 HD, 114,000 mi
when i start the truck i hear click click click coming from under the dash this is intermittin could it be because i used the signal light when i pulled in and parked and the rely is sticking open the ticking goes on for about 20 or 30 seconds after i start the truck
Visitor, 2002 GMC Sierra 1500 HD, 235,000 mi
replaced flasher relay. not fixed
Visitor, 2001 GMC Sierra 1500 HD, 183,000 mi
Replaced switch, problem solved.