Let's try to narrow it down a bit then.
Next time you're driving, and you're hearing the squealling noise (if it's safe) put your 7 in neutral & coast & see if still hear the squealling.
That was we can maybe eliminate the driveshaft & rear end.
Also, while your coasting in neutral, rev the engine a bit & see if the sound of the squealling changes.
Does the sound change if you're turning left or right?
If you put the brakes on, does the sound change?
I'm just trying to get a little closer to what's causing the noise.
2000 740iS. MKIV, 16x9, DDEs controlled by Euro fog light switch, reversed steptronic +/- pattern, paddle shifters, clear corners, Basslink, iPod video with stereo audio, TV tuner, gauge rings, ///M pedals, backup camera with 'on demand' switch, quad brake lights, Dinan engine & tranny software, windows/sunroof close via remote.
2003 540iS. MKIV, 16x9, PDC, CWP, TV tuner, backup camera with 'on demand' switch, paddle shifters, windows/sunroof close via remote, iPod video & audio.