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Mr Hagg · 01-30-2020, **(Subject: engine rattling )**

Interesting. Could be one of the injectors is over fueling when it sees boost. DO bubble test and see if you have a bad injector... But to me a over fueling injector would have more of a knock sound than a rattle though.
What kind of truck you driving? Just thought about one we had was a 379 peterbilt when you started pulling it would rattle end up the clutch was tight and had a harmonics coming from driveline under load up through the clutch linkage. We greased and adjust clutch linkage noise went away.
As far as valve rattle I may be wrong but I dont think those will matter under boost or not.
Also had one that had a random rattle under valve cover and the jake rocker was the issue where the detent on the rocker shaft was worn very bad and it would allow the jake rocker sit there and slap the camshaft every now and then...
This is just a few issues I have seen. If you find what it is please let us know this is very interesting.