Grinding or rubbing noise from the rear

Putting 2&2 together...a couple weeks
ago I found a screw lodged in my left
rear tire. Not knowing better, and in a
rush I put fix a flat in my tire and have
been repeatedly replacing the air as
needed. Little did I know that this
would have such a huge impact on  
the function of my car. Although the
only Indictator light is the low tire
pressure light, there is now a major
Loud rubbing and grinding noise in the
rear that is there all of the time, not
just when I turn corners or brake. It's
been going for about 3 days now. I
stopped driving it. Since its AWD, I'm
assuming that since I cannot repair
the fix-a-flat tire, that I will have to
replace all four tires. Ok, I understand
that, and it's probably time to do so,
but, this grinding....is this the
differential fluid?  Perhaps The
disrepaired tire has thrown off the
mechanical function of the all-wheel
drivetrain? I dont believe the diff fluid
has been changed since the car was
born in 2015, but does this noise
sound like damage?  I'm just trying to
get a good honest opinion before I go
out here and lay out all the money that
I'm probably going to have to spend. I
cannot do the work myself. TIA