Without hearing the noise it's difficult to diagnose. One thing for certain is that if it's the dippers hitting the troughs you have something awfully loose. If you think that's what it is you really need to pull the pan. If a dipper hit anything it's now bent. If it's bent it's not oiling. If it's not oiling you are in trouble. Personally I don't think it could be a dipper if you're still driving the truck but without hearing it anything would just be a guess.

Save a life, adopt a senior shelter pet.
The three main causes of blindness: Cataracts, Politics, Religion.
Name your dog Naked so you can walk Naked in the park.