Power Mac G5 CPU/Bus Speed reduced + extra loud fan issue (coincidence or related?)

Hello, this is my first post here, and to be totally honest I am not a mac man. I've been PC for years. I recently started working for my dad, who does music work with macs, and so I have been getting into them more and more (I like it!).

I have taken over his Power Mac G5 (he got a new one, due to this problem). I'd hate to just toss it out if there might be a solution to the problem.

These are the CURRENT specs:
Machine Model: Power Mac G5
CPU Type: PowerPC 970 (2.2)
Number Of CPUs: 2
CPU Speed: 1.15 GHz
L2 Cache (per CPU): 512 KB
Memory: 2GB
Bus Speed: 285 MHz
Boot ROM Version: 5.1.5f0

What should be different (according to my dad) is:
CPU Speed: 1.8 GHz
Bus Speed: 866 MHz (something around that area)

So here's the issue:

A couple of days ago, my dad started up his G5, and while starting up one of the fans just started screaming super loud.
He tried resetting some of the buttons inside (which, for the life of me, I can't remember the names of what he did), and it made a difference for all of 20 minutes.

My main question: What would be the cause in the drop in CPU/Bus Speed? Faulty processor? Bad heatsink? Dirty fans?

My second question: Is the drop in CPU/Bus Speed related to this fan noise? (I've read a lot of the hardware issues, and it seems the jet fans are a relatively common problem).

I've had it open for most of today, I've dusted out as much as possible (in the fans, the heatsinks, etc), and there is next to no dust in there (there's still gunky stuff, I don't think my dad opened it and cleaned too regularly).

For starters have a look at this article about setting Processor Performance and the Energy Saver Control Panel in Systems Preference. From what you say sounds like your Dad has adjusted to G5 performance.:-

G5 Processor and Bus Slewing - Mac Forums

I've looked into a little tweaking of the performance of the processors, but it should be standard Automatic, (it was when I checked it earlier today), and my dad kept it at Highest, before it went out.

I find it hard to believe that the fan would be working overtime for Automatic, but not for Highest? Maybe I'm wrong.

Thanks for the response though, I'll read up some more in that thread.

EDIT: Re-read what I posted, and I wanted to clarify.

When my dad had it set to Highest, the fans sounded identical to when I ran it with Automatic a few days later. Also, the numbers for CPU/Bus Speed were identical on both settings. So my guess is that this is not the problem. Again, I may be wrong. I'm still new to macs.