Before you go changing the tensioner, reread the post.
The simple problem can be [ and most of the time is }
the Shock Bushing.
Much easier to change than the tensioner.
And less $$$.

Look 2" to the left and 3" down from the thermostat
housing. You will see a bolt that goes through the eye=
let of the shock and into the head. That is where the top bushing is and if you put a little pressure on it when it is rattling, the rattle may stop.
If it does , simply change this shock. Not the tensioner.