Noise on vga output while hdd is active

Hy i have one probably hardware issue.
I have laptop HP nx9420(Its 4 years old) with ATI x1600 mobility graphics card.
Normally everything runs ok with no problems and on laptop lcd panel there are not any interferences of any kind. But when i connect external LCD via VGA cable to laptop, i can see like white noise wave patterns on screen it is not very intense at native 1920x1080p resolution, but when i lower the resolution to 800x600 i can see that pattern very well which is even more visible while hdd is active and/or when i play games/do intense things.
The same thing happens at work where i have 20-inch Dell LCD(i dont remember the mark) and another VGA cable. I tried the same thing on third 17-inch LCD monitor ACER AL712 with third VGA cable which also makes the same thing.

First i was sure it some kind of ground loop so I tried to unplug laptop from AC but it didn't changed anything.

By default i run WinXP where i firstly noticed this problem then i tried same thing on Ubuntu 11.04 but the problem persists.

All tested monitors are working normally with other machines/laptops

This thing happens only on external monitors. Sadly i can't try the DVI output or second VGA output on my laptop because i don't have dock.

"Modifications" made on/at laptop.
added 1GB stick of RAM 3 years a go
replaced dead charger 2 years a go
replaced dead battery 2 years a go
replaced old 100GB Seagate HDD with newer 500GB WD WD5000BEVT 2 years a go.

Any idea or help would be greatly appreciated.
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  1. Well one thing i'm actually shocked about is, your telling me that a 5 year old video chip running 1920X1080p so smooth but when you lower the resolution to its lowest. you could either try setting the resolution to a medium rank. like a popular one is 1600X900 or eve 1680x1050. While i'm sure money may be tight. i suggest you Get a newer laptop with a discrete GPU in it. Just for example i recently replaced my mothers 4 year old Hewlett packard it had about the same ATI card but the memory was what made it soo slow. She now has my last computer( store purchased) with a GTS 450 and 6gb of ddr3. Like anyone, She could tell a bigg difference. I build all my systems now. Just because its a really good experience. But being mobile and effective is good. if your a medium to heavy gamer i suggest getting a Gaming laptop, i know people that use that as a work laptop and game on it at home!, good for those "Long weekends with the family"
  2. this ATI X1600 mobility is discrete GPU and have 256MB descrete memory. It can be replaced the same way as CPU is. BTW nx9420 is 17 inch business class laptop and can handle almost everything from compiling lots of code. I can run videos on full hd resolution(on vga output, "internal" screen has 1680x1050 max resolution) with no problem and play new games ok i admit games on lowest settings, but the problem here is not slow, laggy response in windows but the noticeable flickery noise interference with EVERY supported resolution i really mean EVERY. Native resolution of laptop panel is 1680x1050 where picture on screen is ok.
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