I not sure about the noise -- Personally I can't hear high pitches. I am also a little confused about how you described it changed.
i do however have some thoughts concerns about the weak test light that is now bright.
1. The dim test light is an indication of reduced current available to operate the light.
2. Current flow goes down when voltage goes down or resistance goes up.
3. Because the other fuse circuits can supply enough current to make the test light bright then the problem also has to be something that would only effect the fuses in question.
4. Because the other fuse circuits share the same voltage source, the problem cannot be a reduction in voltage - the circuit in question must have unwanted/increased resistance. (possible loose connection)
5. This leaves anything in the highlighted section of the wiring diagram I enclosed as suspect. Also a possibility it is low current side of relay #42 -- causing the relay to cycle rapidly. Not common as the low current side will typically either turn the relay on or it cant turn the relay on. Does not typically cause a flicker.
6. If it were my car I would replace relay #42 with a new one and see what happens. I would also make sure that the bolts that holds the fuse box together are snug (plastic connectors on other side DO NOT over tighten). If problem reoccurs - start tapping/wiggle fuse box and relay trying to get it to run.
I would not want to swap relay #42 with only other relay in underhood fuse box that is the same because it is starter solenoid relay and if relay acts up again car still wont start -- I don't believe any others (including the rear fuse box) are the same part#
One of the conditions I noted that could set the codes was low system voltage -- the unwanted resistance would not allow throttle module to operate correctly (it would create an unwanted voltage drop to the module)
Just my thoughts -- really hard to diagnosis long distance without touching, feeling or testing myself
Again congrats for getting it running //
Got to make you wonder - did the previous owner have some fuse box/electrical problems - and that is why you found an extra relay and fuses?