1023E Yanmar Engine Noise

Hi, I'm new to this forum and new to owning a subcompact tractor. I previously owned a 1997 JD425 with a gas engine and recently traded it in for a used 2015 1023E with 165hours. I questioned the engine noise coming from the Yanmar diesel at the time of purchase, but the JD Dealer I purchased from said it was normal on the Yanmars. I'm not familiar with the Yanmar diesel engine but familiar with other diesel engines such as Detroit's and Cummins.

I hear what sounds like valve chatter or ticking/knocking in the engine when starting and running the engine at low RPM, I can't hear it at high RPM due to the overall noise of the machine. Just to be clear, I'm not referring to the fuel pump ticking at startup, I'm familiar with that noise. I did ask another dealer about the noise and they said to monitor the temperature and everything would be ok if it doesn't get high!!

I searched this forum and didn't find anything specific to 1023E Yanmar noise or ticking sounds, maybe I missed it.
Is this normal for the Yanmar diesel engine? Should I be concerned, even though the dealer said it's normal? Has anyone else heard similar noise, if so, was there an issue?
Thank you for the help.
Carmen