MBP behaving "weird", many symptoms- don't know the cure

Question

Hello all and thanks for reading this.
Bought refurbished from Apple on 12/2007
15” MBP Santa Rosa
Mac OS X V 10.5.8
2.2 GHz Intel core 2 Duo
4 GB memory
Backing up 2 with Copy Carbon Cloner+ Time Machine to 2 OWC 1 TB Mercury Elite Pro "Classic" Quad Interface
I don’t know if the following info is relevant to solve the problem, but I surely hope so…
About 2 wks ago noticed some kind of noise inside for a while, it looked to me that it was coming from the HD (Fujitsu MHW2120BH, Available 28.92 GB), it was like some kind of rhythmic clicking noise. Went away after a while, back for a little while after about a week.
Then there were other "abnormalities", not all at the same time, so, whenever one of them occurred I either rebooted and it solved the problem, or it just stopped. Sometimes the computer was just sluggish and/or "delayed" (when typing/copying and pasting and so there was a short delay), other times the fan was overworking, others the memory was full too soon, windows, or part of them froze for a bit (or longer), the CPU was working very "hard", my computer is set up to wake up in the morning and lately instead of doing that, logging and start apps, it freezes at the “purple northern lights screen” (need to restart), and so. Since each of those can be acting like that while everything is OK, and then getting back to normal I wasn't worried, just monitoring.
At this moment, I am not running any "hungry/heavy" applications. I have Firefox with 2 windows open and about 20 tabs, none of them running videos or any other heavy graphics, Word, Excel each of them with 3-4 documents, none with heavy/consuming stuff, 1 Password and VMware with Windows XP and Palm Desktop running.
This "load" shouldn't be a problem usually.
Currently the CPU is working on: User around 57%, System 16%, Idle 37%, the fan is CONSTANTLY running on higher speed (both, L & R around 6000 RPM), Temps: HD 106F, CPU 202F) and memory: Wired around 800MB, Active 2.04GB, Inactive 376MB and Free 830MB.
I turned the computer off, let it cool for some hours and just turned it on again without any apps running except Word. Currently the CPU is working on: User around 1-4%, System around 2-4%, Idle around 92-97%, the fan is running at (both, L & R around 2000 RPM), Temps: HD 92F, CPU 102F and Memory: Wired around 450MB, Active 600GB, Inactive 70MB and Free 2.9GB.
Any direction I can take, any suggestions will be very appreciated.
Thank you in advance.
Saul

Answer 1

Thank you all for the advice. I appreciate it!
"I would replace the hard drive, as most, if not all, the symptoms point to that."
Louie and BB, thanks. It's the first thing I thought. Since it started I started backing up twice a day instead of once a day and decided that if that is the problem I will let it die, unless all the other stuff around will be too much to put with.
Allan, thanks.
"Make certain that Activity Monitor's "Show" window reads "All Processes"
It does.
"Two big hitter are unneeded virus protection programs and third-party automated backup schemes. I don't find that Time Machine contributes to this mayhem."
No virus protection programs.
I do now twice a day backups. For the 1/2 hr. that it takes I quit Fire Fox and WMware (2 quite resources hungry apps) and for this 1/2 hr. or so the fan goes up, but when the bkp is done they get back to normal.
(Since I wrote this post the MBP went back to it's "quiet/nice" behavior)... (?!)
"...FireFox with all its bells/whistles seems more taxing than Safari or Camino"
I am sorry, but I don't succeed to get used to Safari (tried, but...). It may be something I "brought" with me from my PC-user-times.
"...physical arrangement of the computer and your usage patterns... The case bottom is part of the heat dissipation system and needs need air."
I indeed use it on my lap, but between my lap and the MBP there is a Lapinator Plus (using it for about 3 yrs and just LOVE it!!!)... .
In addition, I glued 4 (in each corner 1) 3/8" rubber spacers (come w/the Lapinator) AND in addition the back is resting on a 3/4" pad. So, there is plenty of air underneath (which, of course, doesn't mean that the MBP doesn't get hot from time to time (after all it IS a MBP)... .
If you also think that all the other stuff, beside the noise may be just part of the HD problem, then I will start relaxing. I am worried that when the time will come I will replace the HD and it won't solve the problems.
Should I start relaxing, or start worrying?...