I have a '73 1800ES and a '58 445, but my daily driver is a '99 Audi A4. I've never had any trouble with front wheel bearings on a Volvo as they are exceptionally sturdy, but I feel qualified to post given my experience with the Audi. Due to poor design (poor sealing), the rear wheel bearings on my Audi have been replaced 3 or 4 times in 97,000 miles. (I now have the special tools to do this, so I can do it myself). The symptoms of a failing wheel bearing are a slight rumble which increases when you turn away from the wheel that has the bad bearing. What is interesting is that it only takes a very small imperfection in the bearing race to cause a lot of noise. I don't see how the failing front bearing could cause a hot diff, but I can certainly understand how the noise from a bad bearing could be mis-interpreted as coming from some much different part of the car, such as the tranny.