Rattling noise when accelerate up hill and from park

I have a 2001 Chevy Blazer, 4wd, 85k miles. I’ve been getting this metallic rattling sound when I drive up hills and start driving after being parked. It’s not all the time, but generally when I accelerate. It sounds like it is coming from the rear somewhere. Any ideas?

Maybe spark knock? Try higher octane.
Maybe a rattling heat shield or other part of the exhaust system?

Here are a few rattle fixes I’ve used on my 2000 Blazer.

  1. Make sure the the roof rack cross rail slider knobs are tight. These knobs are at each end of the cross rails. A loose knob caused a rattle from the back of the truck.

  2. Check the hood hinge bolts for play. Chevrolet has tapered washers to eliminate any play in the hinge. When the hood rattles it sounds like the dash is going to fall in your lap.

  3. The Blazer was making a metallic buzzing noise under acceleration. I traced the noise to the accelerator cable. When the intake manifold gasket was replaced, the dealer missed one of the tie down points for the cable near the throttle body. One tie wrap later, no more buzzing noise.

  4. Finally try a higher grade of gas in case it’s engine knock due to too low of an octane. I’ve had a few cars that needed midgrade as they got older.

Ed B.

I’ll bet my morning muffins it’s pinging. It has the characteristics.

When was the last good tuneup?
Is the CEL light lighting up (it should be)?
Has anyone looked for fault codes?

Agree with circutsmith, check the heat shields on your catalytic converter and other shields that might be on the exhaust system. I had a similar sound on a car and found the spot welds that hold the heat shield had failed on one side and not the other. At certain times the exhaust would resonate and the loose heat shield would rattle, it was a pretty loud noise. Pretty easy to check when the exhaust system is cool.

I haven’t had a tuneup since… 30k I think. But there’s no CEL and no fault codes.

I know its not spark knock because I just replaced my spark plugs and they were perfectly clean.