I don't know what it is. When the engine is idle, it goes along with the piston slap noise. When I put it in drive, it becomes more constant. It seems to be coming from outside/around the intake manifold.

 

Exhaust leak??

 

if it sounds more metalic than it could be lifter tap

 

If it's an M6... have you over revved/missed any shifts lately?

 

You dont put m6's into drive

 

I just caught that

See if you can find a specific area that the ticking is coming from... I borrowed an automotive stethoscope from my uncle and was able to narrow down the location of tapping on mine to the #3 cylinder area. It turned out to be a failed #3 intake lifter.

 

Now that I think of it, it's more of a grinding/clicking noise...