Garageband Amp Models get noisy?

Hi I was just wondering if anyone else has found that Garageband gets noisy when using the Amp Models to record guitars? And what's the best way to get rid of the noise, while retaining the wanted sound? I definately know it's within Garageband and not coming in externally.

Some background:

I've spent the last few days looking over my setup (which is pretty simple) for the cause of the background noise in my recordings and think the Amp Models in Garageband 6.0.5 (428.5) are the culprit!!

All I have is a M-Audio FireWire Solo connected to my MacBook Pro over firewire. Everything else disconnected, even guitar and headphones. The signal-in is clean which I have verified using M-Audio's software which has no sound on the input monitor scale. However the output monitor scale shows quite a bit of noise on output, which is coming from GarageBand, and can be heard as a hiss. Also as another test, zooming in on a clean recording in Audacity reveals absolutely no waveforms in the silent parts at the start of a recording (I left it recording silence for a few seconds to varify).

Amp models like Ominous Crunch, Stadium Solo, Woodstock Fuzz, Punk Rock and Industrial Overdrive, seem to be the worst for me, especially when turing off GB's noise gate, which I generally dislike.

Using a Real Instrument track instead of an amp modeled one, is acutally quite a bit better, seem's to produce a cleaner input tone? Would this be right? However, adding some amp effects like Big Wheels, British Overdrive or American Overdrive starts to get noisy again, but not as bad as what I'm getting from the Amp Models / Stompbox method.

I've heard home GB recordings online and on youtube that have overdrive/distortion on the guitars but sound clean, the noise I'm getting muddies the tone a bit especially when layering tracks.