Notebook, Hum and Ground Lifts

I have a Dell Inspiron 9300 and have had issues with a loud hum
entering into my recordings when I power the notebook with AC power.
I initially discovered the problem when using the Presonus Firebox (4
pin to 4 pin firewire). I do not have this issue at all when it is
being powered by batteries. It is also interesting to note that if I
use a DI box and lift the ground on it, the hum goes away. Lately, I
also discovered that if I simpy use the mic/line input on the notebook
and run an output from my mixer, I also get a terrible hum. I have
done some reading on the internet and in general it seems that this is
either caused by a ground loop or from the AC power being converted to
DC power. I can't try my DI box because it only has a XLR output
which doesn't connect to the notebook. One "solution" I read about
that seem to work for about everyone is to use the 3 prong to 2 prong
AC conenctors which removes the ground on the notebook. I don't have
a good understanding of electric and was wondering if someone could
answer some questions for me.

1. Poeple say this is dangerous- is it really dangerous if I am
running a line out from my 3 prong grounded mixer to my now 2 pronged
non-grounded notebook? In my mind it seems that as long as the
notebook is connected to something that is grounded then it shouldn't
be that dangerous.

2. In what situations is removing the ground dangerous?

3. How is using a DI box to "lift" the ground better than removing
the ground from the AC adapter?

Thanks,
Andrew V. Romero

.

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