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2011 Chevy Malibu LT 2.4L 4cyl 104,xxx miles
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I have searched the forum trying to find a solution to this, but haven't found the exact issue. Wondering if anyone has heard this noise before and if there is any suggestions. Sorry if this is repetitive, but hopefully the sound on video is helpful. I have a Gen 7? 2011 malibu 1LT with the 2.4 4 cyl 6 spd transmission. 104,xxx miles. I bought it used at 74,xxx. I made sure I immediately did an oil change and filter with full synthetic oil and it ran great for about 25,000 miles until recently when I started to hear a high pitched rattle when under load (2000rpms and up but NOT at idle, no matter the RPM), and fairly sluggish acceleration. It almost sounds like a loose heat shield, so thats what I initially attributed it to and kept driving it as I used this daily for work. About 2k miles later I started to hear the timing chain rattling on cold start, so I set this car aside for some repairs, here is what I've done so far:
  • (obviously) new timing chain, guides and tensioners. This completely resolved the timing chain rattle at cold start. New gaskets all around during this job, including head gasket.
  • New plugs and coil packs, as I thought the rattle with acceleration could be pinging/detonation. No improvement.
  • New exhaust manifold, there was a small crack in mine at the typical location. Also replaced the upstream O2 sensor, but this still did not help.
  • Cleaned fuel injectors
  • New catalytic converter. No improvement
  • New throttle body with new position sensor as I started getting the typical limp mode once in awhile. This fixed the limp mode, but rattle was still present.
  • New knock sensor and new MAP sensor

I did take a video, URL below. To me it sounds like a rattling heat shield, but I've searched all around and can't find anything loose that might cause this. Not sure, but I'm thinking it could be any of these:
  • Heat shield that I'm not seeing?
  • Pinging/detonation? I have no idea what this sounds like though, and all of the youtube videos I've watched don't exactly match this sound.
  • Hole in the exhaust somewhere, but the pipe looks good, including the flex pipe.
  • Vacuum leak
  • Possible bad motor mount
  • Transmission issue? But shifting feels good.

I realize it was stupid not to take it to a dealer to have it diagnosed in the first place and I've done all of this backwards, but I had it apart and had the time. Now that I am this far in with no improvement that is my next step if nobody recognizes this sound.

Thanks in advance
URL for video: 2011 Chevy Malibu Rattling
 
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