Very nice radio!
You've probably already found it, but there's a very legible service bulletin on this model available at:http://www.audiophool.cjb.net/Misc/philco_48-482.djvu
You need to install the special djvu browser plugin to view it.
Some of the comments from past posts on this radio say that the ferrite cores in the I.F. transformers are fragile and easy to break. Hope that hasn't happened to yours.
Regarding the squeal at minimum volume: check out the 4.2 ohm resistor to ground at the end terminal of the volume control. If it has gone high in value, or opened, a feedback squeal might result on account of the connection there from the output transformer.
Also ensure that the built-in low impedance antenna is connected to the correct terminals, 1 and 2 it looks like. There is a 3rd terminal that goes to the output transformer. It's there for convenience in hooking up a meter during alignment. If the antenna got connected there, well weird things might happen.