Never got a second opinion after posting video. Bumping so maybe someone can see it

Hey guys,

So I ended up tightening the alternator and AC drive belt some more and I haven't had any squealing whatsoever since, so fingers crossed that problem is dead forever now.

Going back to one of the other main points of this thread - I've been driving with no speakers connected for a while now so that I can listen to the engine noises (trying to spot anything odd). One thing I've noticed is that in the engine bay, there's a whining sound.. very similar to a supercharger winding up/mini-turbo; identical to the whine I would sometimes hear through the speakers.

All I've gathered so far is that it fluctuates loudness/pitch with RPM (same as the speakers) and it's either completely disappearing or it is quiet enough I can't hear it when idling. One thing I was thinking about was that the whine sounds identical to the speaker whine - so maybe this is the source of that issue, and that's why no matter how many times I re-grounded, ran new wires,etc. on the speaker end, I couldn't eliminate it.

I asked on a Facebook page and someone said that they had a similar issue in their Hilux, and it turned out to be their external alternator regulator. Can anyone elaborate on that? Does the MR2 have an internal or external regulator? And would that likely be the issue?

I also read this article and I feel like maybe troubleshooting the "Circuit causes" section might be worthwhile

Did some further researching, and I believe possibly one of my diodes may be faulty in the alternator - I'll try and get my hands on a multimeter soon (may have to buy one) to figure it out. Not sure if I'm testing it the right way, but I'll be testing for AC voltage at the battery. I'm assuming that if I get any one of the diodes must be on it's way out.

Can anyone confirm if thats the way to go?

You'd need a pretty good multimeter to "see through" the DC to check if there was any AC present. It does sound like alternator problems. remove the belt & see what happens! But don't run it too long.

A good auto electrician can confirm if something is wrong with your alternator. They can rebuild it if it's a genuine denso.
Other than an autoelectrician, best advice don't play with it.

Swore I posted again..

I'm 99% sure that my speaker whine issue is due to a ground loop (blown pico fuse in the headunit maybe?). All I know is the RCAs need to be grounded - so, I'll be visiting Jaycar tomorrow to buy some goodies to sort that out.

As for the engine bay whine, no idea. I thought my interior and engine bay whine were related (as they make the exact same sound) but unfortunately, that doesn't seem to be the case.