Mercury grand Marquis growling/voltage

I have a Mercury grand Marquis 2005 the battery
light was already coming off  but then one day The
water pump broke and bent down pretty good I
replaced the water pump belt and Idler pulley . After
doing this the car started growling and the voltage I
would go down at the same time and back up again
after the growling stopped while the car was in
reverse or idling at red lights. It does not do it in
park or well pressing the gas driving only when it
slows down to a complete stop and idle it does this
in reverse no matter what.  So then it would not
charge so I replaced the alternator, being a cheap
rebuilt AutoZone alternator can you start acting up
in about a day.  It started doing the growling and
low-voltage thing during red lights and reverse it
seemed to only do it at first with the AC on and I
was able to keep it from happening with the AC off
except while in reverse.  You can run anything on
full blast and do whatever you want while the car is
in park this will never happen. It started getting so
low voltage the car almost stalled so I replaced the
alternator again me and it stopped for  a few hours  
then once again it started growling and the voltage
went down at red lights and reverse , so then I
focused on the belt tensioner since the belt I had
developed a white line on the side . Changing the
tensioner made it stop for a day and a half then one
day in a drive-through when I stopped it did it then
got worse again the battery light has not come on
with this again and it seems to be worse one day
better the next for the first time the other day it did
the growling noise and voltage with the AC off at
idle I was able to keep it from happening before
with the AC off at lights , If I fed her the break when
it starts to do it it will stop and sometimes if I stop
slowly it will not do it. Again it will not do it in park
only in drive while idling  and in reverse. The other
day I went around the corner and when I pressed
the gas to go again it hesitated growled in the
battery wouldn’t charge more than halfway until I let
off the gas and pressed it again and everything was
normal. The other night the battery was at halfway
and would not charge then when I turned the car on
after work everything works normal and the charge
was up until red lights. I am very confused and
frustrated with this one because every time I
change some thing it seems to make it stop for a
period of time.  It’s a great car it has been taking
great care of oil changes and all again we never
had this problem until the water pump broke. Does
anybody have any suggestions what  this could be I
am about to change all the pulleys  and the
alternator again.  Thank you Sorry for the typos I
type this all out the first time and it didn’t post it so I
got frustrated and don’t care to change them