I have 2011 GMC Sierra , 5.3 engine, 163k miles. I have been hearing a ticking sound at startup for a long time - maybe 2-3 years. I'd sometimes hear it, sometimes I didn't. Here lately I have noticed at each startup but it goes away after its driven some. So, I only hear it after startup (at idle) until the truck is driven a few miles. I've always used 5w-30 oil as recommended. I know the AFM (Active Fuel Managment) is the culprit and its quite common in these engines to have lifter failure. I just changed from Castrol Dexos 1 synthetic to Mobil 1 High Mileage, and added Lucas Oil Stabilizer thinking that might stop it. The tick is still there. I'm wondering if going to 10w-40 oil in this engine would be worth a try.....or would that damage the engine somehow. I bought a jug of Castrol Synthetic Blend 10w-40....but before I put it in I thought I better seek advice. Any knowledgeable help will be appreciated.