1999 GMC 2500 motor knock

[SJClark0529]

My pickup has developed a knock… well, I guess it’s more of a ticking noise. I only hear it while accelerating, but not all of the time. Typically it will be obvious when I begin accelerating and sometimes with the throttle held at the same spot, it will go away until the throttle is released and applied again… but not always. Any ideas?

I’m hoping it’s not a lifter knock.