The round mechanism at the very front of the engine, connected to the crankshaft by the crankshaft gear and turned by the serpentine belt is making a noise.

 

What your describing is the harmonic balancer.
Ken

 

Some description of the noise would be helpful. I would release the tension on the belt, then grab it and wiggle it to see if it is loose.

 

You can also eyeball it and see if the serpentine belt looks like it is in proper alignment with all the other pulleys and idlers.
There have been some cases of the crankshaft pulley getting loose and even falling off.
Not good - that's a lot of spinning mass to have running loose in the engine compartment, not to mention the loss of power steering, alternator and water pump.

IF IT'S LOOSE, DON'T DRIVE THE CAR !!!!