1999 GMC Sierra knocking sound in engine

Hello,

When did this start?

A couple possibilities.

Spark Knock - Try Higher Octane Fuel

Timing needs attention - Check timing,

Also when was last tune up Cap, Rotor, Plugs and Wires.

And if haven't had timing chain changed it is probably time.

Another possibility is a weak Oil Pump, check oil pressure.

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It does not sound like the engine to me, it sounds like you have drivetrain problems, first of all get underneath your truck and check all of your U-joints to start with.

I would almost agree Dr Loot if it wasn't stated that "It also makes the noise continuously if I'm parked facing up a steep hill." How would it be making the knocking if standing still.

However, more detailed info on the problem would help out a lot.

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I believe your truck has an anti-knock sensor on the right side of the block by the starter, it is round about 2 1/2 inches in diameter, with one wire going to it, it's supposed to work under load only, so get on Mitchell 1 and find out how to diagnose it.I got on Mitchell 1 but I cannot find anything on the anti-knock sensor can you check and see if you have one on your truck? And get back to me.

The Knock Sensors are located in valley under Intake Manifold... This is the location for both 1500 & 2500 series and all V8's....

Here is Test Proceedure....

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O.K. You don't have to kick my A$$ I'm just trying to help. It must not be a knocking sound it has to be a backfire? The only other thing it can be is the cam or a bad lifter or a valve, sorry Loot Bug, it's like the blind leading the blind, if I could hear the noise, maybe I could come up with something, if I can help let me know.