Problems with hard drive

[hackett@gaul.csd.uwo.ca (Mike Hackett)]

Well, it looks like before any of this tape backup or SCSI test software
that I've been asking for (and am still interested in) won't be of much
value to me just yet, as my hard drive seems to be flakin' out!  Arggh!
Talk about bad timing!  I'm hoping someone here can give me some pointers.
Here's my situation:

Based on sound alone, it seems to me that the drive is having trouble
maintaining its proper spin rate.  It's familiar startup sequence of
gradually rising pitch as the drive spins up doesn't always complete, 
and often the drive's "whirr" (I don't know how else to describe it - 
you know what I mean) seems to drop in pitch and then slowly work its
way back up.  When the drive is running at the proper speed, all of
the data seems intact (thank goodness), but it's so flaky that a second
"ls" right after a successful one, often results in an empty directory
listing or an I/O error.  Sometimes the entire hard drive, all of the
partitions, just disappears from the system's table.

My uneducated guess is that the problem is a faulty power supply, which
would probably be the best possible scenario, as replacing that should
neither be difficult nor too costly.  But before I do that, I'd like to
get a more knowledgeable opinion.  My other concern is that the drive had
been working flawlessly for 2.5 years up to now, and the problems started
at the same time as I tried to add my new Wangtek tape drive to the chain.
Now, I can't see how the hard drive could have been affected in this way
by the addition of another device, even if improperly hooked up (which I
don't think it was - see my earlier post about SCSI test software), but
maybe someone in this group who knows more about these things than myself
can offer an explanation and help me avoid any future problems.

I welcome any email responses, or post stuff here.  I really need to get
back to work, which requires that my hard drive be back up and running.
I do have most of the data backed up, but without a hard drive, I'm unable
to do any development anyway.  As I said, the data seems fine, so really
hope the drive can be saved.  Sorry for the length of this post, but I
wanted to provide enough details for someone to help diagnose my problem.
If any further clarifications are necessary, please drop me a line.

Thanks in advance.

Mike