When my engine is under load, and I press the accelerator, there is a very brief (maybe one second), faint, muffled rattle. Like a diesel engine. Especially when going uphill. It doesn't happen in P/N. Is this normal?

2013 5.3L with VVT
(71,000km/44,000mi)

 

Few questions:

1. Has it always done this? if not, when did it change?

2. Have you had or done any work on it lately?

My van was making a rattle like this. It would happen at a specific RPM under load. My first thought was valve clatter or pre-detonation so I put in the high octane fuel with a booster additive but no change. I checked the timing and while the dog house was off drove around and listened.

I started touching everything in sight and turns out the noise was a loose A/C bracket bolt. I guess the previous owners mechanic forgot to tighten it. At a certain RPM the harmonics were just right and drove me crazy.

Just a possibility... could be something loose.

Good luck
John

 

1. Hard to say. I've been driving my van a lot more than usual lately. It might be a new problem, or it could just be that I have become more attuned to its sounds over time.

2. The only work to the engine I've done during my ownership (last 12,000 mi), is replacing the oil + filter, air cleaner and coolant. None of them lately.

I think if there were a loose part related to RPM, I would also hear it in Park or Neutral, as well as while decelerating. The engine doesn't vibrate a great deal either.

 

Consider taking off your AC belt and seeing if that helps. It could be A/C slugging which is described in GMC 03-01-38-019a.

 

the bulletin applies to vans from 2002 - 2004