Macbook won't start-up, disc noise, intermitent

A family member has a Macbook with an issue.

From a powered down state, when the power button is pressed, the Macbook will not start. It 'hangs' and makes the disc eject noise continually. I know it's a normal sound to hear once, but this is happening continuously. It does not stop until the power button has been held down to force an immediate shutdown.

This problem is intermittent, and is slowly increasing in frequency. Usually, the Macbook will start and boot like normal, but just sometimes it does this. It's like hit and miss.

My hunch is the disc drive is faulty. It will cost over $100 in parts for an Apple-labeled disc drive. More than she can afford. I will do the labor on the laptop, as I've worked on Macbooks and iBooks in the past. Also, I'm CompTIA A+ certified, so the labor is not an issue.

First, I'd like to reset the NVRAM. I am 85% certain it won't fix the problem, but it's better to try than throw money away at parts.

Does anyone have any ideas what else could cause this?

Also, are there any less expensive alternatives for a slot-loading combo drive?

* UPDATE/EDIT *

My original post included the following quote as text. I just talked to her today and she says that the following symptom hasn't happened since I replaced the hard drive:

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She has also complained that the Macbook will make this sound and the system will freeze. This happens when she is using it, for example to write an exam paper or listen to MP3's.
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Click to expand...

Also, she seem to indicate the Macbook will sometimes make the continuous disc eject sound when opening the lid from a "Sleep" state.

More importantly, she says the Macbook will not boot at all today. She seemed to imply that it's toast.

Here are some links for parts I want to make note of:

$149.95 - Used - Macbook 13" combo drive
Product code: IF186-024-1
Apple Part #: 661-3905, 661-4090, 662-4287, 661-4490
MacBook 24x Combo Drive (661-3905, 661-4090, 662-4287, 661-4490) - iFixit

Will this work in a Macbook?:
$34.95 - Used - iBook/PowerBook G4
Part Number: 661-2579, 661-2690
Combo Drive 8x iBook G4, PowerBook G4 - 661-2579 - Mac Recycling

$149.95 - Used - Macbook 13/15" SuperDrive
Part Number: 661-3906, 661-4091
SuperDrive DL 4x PATA MacBook/Pro 13"/15" - 661-3906 - Mac Recycling

Will this work?:
$97.08 - 9.5mm thick - DVDRW/CDRW
www.span.com - DR9Npan867 - UJ-867-B - DVD +R9 Dual Layer Double Layer Desktop, DVD+R9, DVD-R9, Multi Drive, Notebook multidrive, Slimline Multidrive - Panasonic Notebook 9.5mm Slot-Load UJ-867-B 8x6x DVD, 24x CD, 5x DVD-RAM Black

$60 - Used - Ebay - DVDRW/CDRW
Apple MacBook A1181 CD-RW DVD-ROM Combo Drive CW-8221-C - eBay (item 390023552706 end time Jan-14-09 18:51:03 PST)

$64.95 - Used - Macbook 13" - Out of Stock
Combo Drive 24x PATA MacBook 13", MB Pro 15" - 661-3905 - Mac Recycling

$107.77 - NEW - Macbook 13" combodrive
Apple Part Number: 661-3905
http://www.macproonline.com/Shop/Control/Product/fp/SFV/32645/vpid/5636886/vpcsid/0/rid/129150

I might suggest, if you can get the MB booted, to boot from the install CD/DVD and verify that you are not hearing the HDD begin to crash. Never hurts to check. You might also try removing the optical drive all together and see if the problem goes away - sort of isolate the issue to one piece of the architecture. As far as prices on new hardware, Google is probably your best friend at that point. Good luck.

XJ-linux said:

I might suggest, if you can get the MB booted, to boot from the install CD/DVD and verify that you are not hearing the HDD begin to crash. Never hurts to check. You might also try removing the optical drive all together and see if the problem goes away - sort of isolate the issue to one piece of the architecture. As far as prices on new hardware, Google is probably your best friend at that point. Good luck.

Click to expand...

Yes sir. Actually, the hard drive was failing. A few days after Christmas I replaced it with a WD Scorpio 120Gb. It is very fast in comparison to the stock hard drive.

The optical disc drive problem started occurring before the hard drive was replaced. It was less frequent. The first suspicion was a year ago +/-.

I need to bump.

Is there any possible chance the logic board is failing?

Any advice or ideas are welcome.