Grinding/rattling noise from under the hood

Hello everyone!  So I'm having
some issues with my 2013
Avenger SXT (I know, I know...big
shocker, right?).  Anyway, I had
the alternator replaced a couple
of weeks ago, and all was well for
a week or so, but then the engine
light came back on.  Then I
started noticing a
rattling/grinding noise coming
from under the hood (passenger
side from what I could tell).  So I
took him to AutoZone and had
them put the code reader on him
and the only single solitary code
he threw was for the thermostat. I
bought the new thermostat and I
put it on this morning. I filled up
my coolant tank, and took him for
a little test drive.  Guess what.  
The noise is STILL THERE!!!!  
WTF??  What else could it be?  
Would he not have thrown
another code if there were
another issue?  I'm at a loss here.  
I had to miss work today to work
on my car and I still have the
issue.  I can't afford to lose any
more pay!  Someone please tell
me something useful. I would
really appreciate it.
Oh!  The noise ranges from a
rattle to a full on grind.  It's not
constant,  but it's very frequent.  It
occurs when I'm driving fast or
slow,  or even just sitting at an
idle. Weird.