M4400 High pitch noise

Why do you say your situation worsened? The noise was louder?
If you got your system replaced because of this, why wouldn't I?

Anyway, are you sure it's CPU? I mean, the noise is not always present and many more things seem to be affecting it. Also, it seems to be slightly less audible under Windows 7 than under Ubuntu.

Oh, and I tried forcing various CPU states - the noise is present not only in the low power mode.

 

Dell won't replace your system just because of a whine. Instead they will send you a refurbished motherboard; and if installed incorrectly you'll end up getting more problems. I had several issues with my laptop, the whine was the least important. After 3 months they finally sent me a brand new system. See if it's very loud running on battery. My whine was more noticeable when running on battery.

 

I'm experimenting with BIOS versions now. I tried downgrading from A15 to A03 and the whine was almost completely gone (just a little when starting Ubuntu), but the fan wouldn't stop. Now I'm on A18 and it seems that it's more noisy than A03 but less than A15. Now I checked it and A18 is more noisy on battery than on AC. However, I think A15 was as noisy on battery as on AC.
I also tried disabling Speedstep and the noise is gone but this is not a solution. I don't want the fan to be constantly running.

Anyway, that's not the CPU that is making this sound, those are motherboard's parts. With my previous (M1530) laptop Dell hasn't messed anything when replacing the motherboard so I might risk anyway. I guess I will observe how often the noise is perceptible with A18 and decide.

 

It could be a bad capacitor or fan squeal.