Strange Fan Noise t40 thinkpad??

[smith07031]

This one is strange: one of my t40s makes a strange buzzing noise like a bad fan only when I pull the ac adapter out??!
It seems when I pressed down on the top of lcd with laptop upside down abt 90degree angle, the noise would go down a bit.
This is not coming from the cpu fan (I think??) as last night this was occurring when I had keyboard off, and had watched cpu fan which wasn't even turning yet? Is there a 2nd fan other then the cpu fan on the t40 laptop?. I have blown all the dust out from the cpu fan and other areas.
It definitely only happens when I hold the laptop on an angle with the rear of the thinkpad folded at a 90 degree angle upside down at a certain angle but Only With ac adapter Unplugged, it makes the buzzing noise. Maybe the Power Management which I have disabled thru services.msc on my t40s.
Your advice is greatly appreciated. Thank you.

[poshgeordie]

Things which come to mind:

1. Do you have a CD in the CD/DVD drive which starts up when it goes to battery.

2. The inverter is noisy. The inverter is located in the base of the display. To check that, connect the TP to an external monitor. Switch to external monitor (ie switch off internal screen) and see if noise disappears.
You can tell that I don't know which F key to press to do this!!

3. Could be the hard disk. Try removing it and start the TP up and go into bios (F1 - know that key!) and see if the noise's there.

4. It won't do any harm to completely remove the CPU fan assembly and properly clean it out. There's quite often hair and 'stuff' stuck inside which is not dislodged with blowing the fan out.
Remember if you do that to renew the heatsink compound between the CPU and heatsink.

Other than that, I suggest you exorsice the thing!!!

<Edit> Added Hdd

[Mike Blake]

2. The inverter is noisy. The inverter is located in the base of the display. To check that, connect the TP to an external monitor. Switch to external monitor (ie switch off internal screen) and see if noise disappears.

You can tell that I don't know which F key to press to do this!!

Fn+F7, the one that has the little icons of a
dark monitor and a lit one. And you don't even
have to wait to install an external monitor to
test if the key combo makes the noise go away.
If there is no monitor attached, you just get a
blank, turned off screen. Of course Fn+F3 is
also supposed to do that (turn the LCD off).

[smith07031]

Thank you will try your suggestions, but then why the minute I plug in the ac adapter, the noise ceases completely?