This morning I noticed a constant knocking sound when sitting still in Drive. I shifted in to Neutral and the sound vanished. Shifted back into Drive and the knocking noise came back. Upon depressing the accelerator the knocking speed does increase. Any idea what this could be? I’m guessing it has something to do with the transmission, as the sound is only prevalent when the Transmission is in Drive. I also just started experiencing the infamous shifting “Squawk/Whoop” and will be doing an ATF flush this week. Perhaps this is a related issue?

I’ve owned this vehicle for less than 2 weeks and these symptoms just began over the last few days…and my check engine light came on over the weekend. Pulled P0128. I’m guessing it needs a thermostat but suppose that’s another thread. The knocking sound is concerning to me. Ideas?

 

I'd start with the simplest explanation first by seeing if the exhaust is thumping against something when in drive, and especially if it goes away in Neutral or Reverse.

 

Also the transmission mount.