Crazy Interference

[Barakka]

Just bought some audio monitors (Yamaha HS50M) and getting crazy interference coming from.... a combination of my laptop PSU and the HDMI connection to the external monitor !?!?

If i disconnect either the power lead from the laptop (not unplug it from the mains), or remove the HDMI connection lead to the monitor the noise goes away.

The sound is full on electrical interference, not mains hum, can hear changes when doing things on the PC, and it happens as soon as the speakers are turned on, even with NO signal connected to them.

My MBP is also connected up but via mDP>DVI and no problems there, only when I turn on the PC laptop.

The HDMI lead was cheap and I have no idea if it's shielded or not, any chance a triple/5x shielded HDMI lead could fix this ? or is it more to do with the mains adaptor ? Don't want to lay out £20+ to find no difference...

[Barakka]

So turns out it's a ground loop issue, to do with the newer laptop PSUs having a three pin connection (with earth) but only two to the laptop itself, which means the PSU is earthed, but the laptop isn't, but when you connect the HDMI lead it gets an earth, hence the loop - or something like that.

BUT I have a potential solution - I have an old brick sized VAIO PSU from a very old VAIO that is the same voltage and connector - but most importantly is a two pin connection to the mains - no earth = no noise

Only question I have is if it could do any damage to my shiny new VAIO running on the old PSU - the new one is an AC19V46 and the old one is an AC19V4 - specs wise they are almost identical though...

OLD PSU
INPUT 240V 1.5A
OUTPUT 19.5V 5.13A

NEW PSU
INPUT 240V 0.7A
OUTPUT 19.5V 6.2A

Anyone know id there's any danger here ? My thought is it will just charge a bit slower with the Old PSU providing 1A less ?