Presonus Firebox Strange Noise on All outputs

When I got no noise from the headphones was from the headphones jack on the audio interface.
Then amp is a regular guitar amp. I use a regular 1/4 inch cable from the Firebox to the Amp.

Regular guitar amps have unbalanced inputs (TS 1/4 inch connectors). The special cable and wiring diagram that I mentioned won't help you because it requires an amp with balanced inputs (TRS 1/4 inch or XLR connectors).

do you mean instead of using a 3 to 2 prongs cable, alter the firewire cable running from the computer to the audio interface?

No, the fireware cable should not be altered in any way. I was talking about altering the audio cable from the audio interface to the amp. Now that we know it's an unbalanced amp, you can forget about this suggestion.

I'm from Argentina and currently living in New York. I know a lot of apartments that are ungrounded (2 prongs). I dont know from anybody who suffered any electrical shock for using a laptop.

Dead men don't talk. Dark humor, but you get my point?

Of course....high consuming devices such as freezer can be very dangerous......but can a laptop be really dangerous?

This is a common misconception. The danger of electrical shock from a device is not related its power consumption. You can be electrocuted by touching a 3 watt night light with a broken bulb. Laptops with external power supplies may be safe (depending on the design of the power supply) to use with a two-prong adapter, but there is absolutely no way that I or anyone else on a forum should advise you to defeat any safety device.

I put eh 3 to 2 pongs adapter in the laptop power supply and the noise disappeared completely. Thank you all.

now the thing is...is it worth that device for 80 bucks?

I looked at the Amazon listing and see that there are two Ebtech devices. One of them is for ac power and the other is for audio lines (1/4 inch phone jacks.) My guess is that the ac power version will not help your problem because it isolates the hot and neutral wires with a transformer but I'm assuming that it doesn't isolate the safety ground. Based on what you've described, the safety ground is part of the noise signal path, so this device isn't the answer. The audio version probably will eliminate the noise because it will isolate the laptop ground from the amp ground, but it is an audio transformer that will color the sound. However, guitar amps are not studio reference monitors, so the effect of the transformer probably can't be heard.

Grounding problems are really hard to diagnose on a forum. (That's why you don't see a lot of other people jumping in here ...) Good luck.