Alright, so I've been playing for a week now and I've noticed,
that my amp produces a prominent hiss sound. So I wanted
to know if that's considered a normal thing or not.

Here's the deal. It's a modeling amp with one 12AX7/ECC83 dual triode
tube somewhere in the circuit. From what is written all over the Internet,
this amp is considered to have a killer sound in it's price range.
Unfortunately, I never listened to the "real" full tube amps, so I don't
have a reference point here in order to compare. But what I have instead,
is a major hiss sound coming from the amp. When I got gain, volume and
knobs at the maximum and tonal controls at 12 o' clock (neutral)
the hiss is at a very-very prominent level. When I switch the modeling knob to
some of the high-gain amps (Marshall Plexi, Mesa/Boogie, etc.) it's like
the white noise in my car stereo when I'm in between of radio stations.

Now, this is unplugged. When I plug my guitar (S/S/S Fender, MIM) and
touch strings it's even more noise which sort of blends with an actual
loud sound. Is this behavior o.k.?....... As a complete beginner that kinda
makes me feel sad 'cause I expected to experience a crystal clear sound,
especially after all those praises to this amp that I read on the Net.

Of curse, when I back my tonal and volume settings to a little bit more
than a minimum it's sounds pretty decent, but what's the point of having
a 100W amp then? Besides, even at low settings you do hear how the hiss
and white noise interact with the actual sound.

I'll be ultra thankful to everyone who'll help me to clarify this situation.
And thanks for you time.
of course it's gonna make some excess noise if you have volume at full, especially on a high gain setting with single coils........
^Exactly, High gain+single coils+high volume=shedloads of unwanted hissy crap.

AND apart from Faith No More, No band ive ever heard uses gain at full, try downing it to around 9 or 10 so its not so saturated.
You've been playing a week, have a 100W amp and a MIM Strat?
The Laney Thread are big and clever. No exceptions.
Thanks to everybody who answered.

And yes, I've been playing a week. I am a beginner.
A little explanation to my gear. I always loved Fender sound,
so I decided to get a Fender guitar. Since MIA Stratocasters
are a little bit expensive, I went for a MIM one. While at the
shop, I found one particularly great sounding model, which
is Classic Series '60s MIM Stratocaster.

While choosing the right amp, I was (obviously) looking for
a great sound and tone. Now, those big real full tube monsters
are automatically out of question, since I cannot drive them in
the quite apartment where I currently live. So I listened to a
handful of solid state amps and none of them seemed good
to my ear. Then appeared a consulter and begun to sing
serenades about this VOX Valvetronix, which basically boiled
down to this:
  • It has a tube in the modeling circuit, thus produces a very
    "tubish" tone, unlike the competition.
  • It has a wattage regulator, so it can be driven in high-gain
    and distorted, yet on a humble 5 watts.
  • It's the best thing on the market for discovering your
    future favorite sound, 'cause modeling
    possibilities are indeed very rich.
  • 100W is great for the clean sound.

Then I came home, read a ton of positive reviews on the Internet and was bought.
Now, however, I'm thinking that perhaps I would be better off with a Blues Junior.