5.0LX BBK Headers,left side tapping noise leaking?

Hi,installed new BBk headers sunday no time to work on car tell next week.I noticed after every thing was bolted in BBk headers to bbk off h-pipe and made sure everythings tight,i start car and heard this light tapping noise which sounds like its coming from values area not sure.Maybe didnt tight h- pipe tight enough to headers could be leaking?What does a leaking exhuast sound like from headers?The noise iam hearing is a very light tapping sound at idle and then u can still here it up tell about 3k rpm then its not noticeable.Thx for help if any.Used evrything from kit of headers to install.