I have a 2006 Sonata that we bought new. We bought it with 50miles and it has always had this knocking sound when your start the car after it has been sitting for a little bit. The knocking last around 5 sec then subsides to nothing. I dont know what it is and although my parents never have taken my advise to get it looked at under warranty they never did. I dont think its normal since I never heard any other Sonata do this.

What is it?

Thanks

 

Has the timing chain tensioner ever been replaced? If not, you probably need to:
https://www.hyundaiforum.com/forum/h...-startup-6621/
https://www.hyundaiforum.com/forum/h...-problem-9019/
https://www.hyundaiforum.com/forum/h...start-up-5570/

Print out the following TSB (Technical Service Bulletin), take it to your dealer and have them fix the problem correctly:
TSB #06-20-002