Mysterious knocking

[CMC2021]

I recently purchased a 2014 Silverado LT and quickly noticed a dull knocking sound coming from the passenger side floor board front tire area. Brought it back to the dealer they put it up on the rack couldn’t find anything loose, they removed the skid plate on the front and drove it but the noise persisted. It does it at random speeds while you’re holding the Excelerator, if you let off or give it more gas it immediately quits, sounds like some kind of plastic knocking on something but cannot find what it is. thought it was the running board or possibly the inner fender but everything is secured. I know it’s a used truck but the rest of it is amazing, it’s the only thing keeping me from loving it.

[pokismoki]

check the trans mount, i found i was missing the hold down nut to the crossmember to trans mount.  take flashlight and shine inside the hole under crossmember, you push up on the driveshaft yoke and see if you lift the rear transmission. if so order the nut if its missing

[CMC2021]

Thanks, will do!