Ground loop problems (Power supply?)

Hi everyone. I have two Dell latitude laptops: E5420 and E6430.

E5420 original power supply 19.5 V - 3.34A (65W)

E6430 original power supply 19.5 V - 4.62A (90W)

Everything works correctly but when I connect the external sound card via FireWire, which is connected to 2 amplified Yamaha HS speaker monitors, with the 6430 I have ground loop problems and an annoying background noise comes out of the speakers, needless to say that it makes any management of the audio impossible.

While the problem does not exist if I use headphones from the sound card.

The problem disappears if I power the 6430 only by battery or with the 5420 power supply.

With E5420 everything works perfectly but if powered with the E6430 power supply the noise returns to the speakers. So apparently the yes/no ground loop variable is the E6430's power supply.

My questions are:

-Is it possible that a power supply that works and charges correctly has some malfunctioning component that generates the noise?

-Is it possible to power the 6430 (4.62A) with the 5420 (3.34A) power supply or can it cause damage to the battery? I knew that the amperes must be equal to or higher than the original ones but I don't know for sure.

If anyone has had similar experiences or has better knowledge than me, any advice would be greatly appreciated. Thank you.