2001 Mustang GT burning rubber smell (with photos underneath)

Hi All. I bought a really nice, clean 2001 GT late July! My first GT!

It's got 49K and a manual transmission. The interior is a time capsule with not a spec of dust.

When I test drove it from the seller almost everything was perfect, drove straight, great brakes, clutch is fine, etc., but it seemed to have a bit of rear end noise, which at first, I thought maybe it was road noise (one tire was missing a balance weight), but then after a while I noticed that it was a consistent whirring at all speeds. So I thought it was a wheel bearing.

I looked all over for any leaks and stuck my head under the car with a flashlight and didn't see anything nasty.

So I took it into a shop to have some general maint., coolant and brake fluid. I told them to take a good look under and around the car for anything that needs attention. They said it was all good... and didn't say anything about the rear end noise.

After a few longer drives at Woodward Dream Cruise, I started smelling something like burning rubber, and it wasn't the tires folks. Wasn't too strong at first, but then this past week it seems to be getting worse. Seemed to be coming from the middle rear of the car, so I looked underneath and noticed what looked like oil or fluid of some sort. I know nothing about the underneath of a car, except for exhaust pipes so pardon my ignorance. Would the Differential be leaking near the exhaust pipes? The photos attached are from the drivers side. And it smells like burnt rubber, which seems like transmission fluid. I didn't notice any drops on the garage floor, but maybe something very slight (not like oil).

Any ideas? I really don't want to take it to a Ford dealer (not too impressed with the one in my area), but I probably should, since they see them most.

Thanks in advance!