I recently purchased an immaculate 96 Land Rover Discovery Series 1
from the original owner.  I noticed right from the beginning that
occassionally I would hear a high pitched squeal coming from what
sounds like either the left front or rear wheel.  My initial thought
was it was a bad wheel bearing but then I noticed it typically started
when I had been braking and then let off the break which led me to
believe it might be a metallic sensor on the pad that drags against
the caliper (I had an old BMW with this feature).  I read that you
could diagnose a bad wheel bearing by excessive play in the wheel when
jacked up so I jacked the rover up yesterday and tried to see if the
wheel moved any direction other than forwards/backwards, seemed pretty
solid to me.  So then I pulled the wheel and looked at the brakes,
they look to be atleast 50% so I don't think it's a brake issue
although I have been noticing quite a bit of brake dust on the front
wheels, perhaps this is just common of Discovery's?

I repeated this process for both left front and rear wheels and didn't
notice anything abnormal.  While spinning the wheel w/ it jacked up,
there is a slight scraping/friction noise but I'm guessing this is
normal??

So now I don't know what direction to take on diagnosing this issue.
Perhaps I could be way off w/ the source of the noise as it's
difficult to pinpoint while driving.  It seems to occur at all speeds
and doesn't change in volume although there is a slight change in
rhythm as if it is related to something that is rotating.  Any
thoughts on common sources of this problem, what else I could look at
etc?  I assume it could still be a wheel bearing and seems pretty
likely but I can't prove it without prying the wheel apart.

I took some pictures of the rotors w/ caliper and the amount of brake
pad left if it's worth anything.  I've done brakes many times before
and I can't imagine the pads are too low, they were replaced about 20k
miles ago according to the records I got from the original owner.  Any
advice would be much appreciated.

Thanks in advance...

Zach