Spirited driving in 4cyl mode? You might need to post some audio files to hear what’s going on, but more appropriately take it to a dealership mechanic, provide him with as much specific info as you can to help diagnose the issue. Perhaps a demo of the sound is in order to help diag the problem.

 

You need a drive belt tensioner, seen it more times than I can count. Have changed three in the last several weeks. Very right throttle on V4 mode sounds like something in the front of the engine rattling.

 

Like I said earlier, you need a drive belt tensioner, the crankshaft pulsations in 4-cylinder mode, causes the rattle noise. Hydraulic tensioner leaks out the fluid, then starts to rattle in V4 mode. There's a GM TSB for this concern also

 

Thanks for the info, any chance you happen to know the TSB #?


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There is a newer TSB 15NA040 for this as well I learned today.

 

Here is TSB 15NA040

 

Just to close this tensioner and belt replaced and the loud noise is gone.


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Just for future reference, I was able to duplicate the noise by: being in V4 and slightly accelerating into V8 mode. 7/10 times it made the rattle sound.

 

Are there any jerks in the transmission?

 

It might feel like a jerk in the transmission at times but it certainly is not the transmission at least wasn't in my case.

 

I

Are there any jerks in the transmission?

I personally didn’t experience any while this is happening.