My Rocket Giotto sometimes, maybe one of 10 shots gives me that loud squeaking sound just after I open the lever and it lasts about a second. The sound is exactly like heavy door in some old witch house. It is at the very beginning of the brewing process and stops when the water enters the portafilter. It is not from the handle as the handle is already fully up when the sound starts.
Is it something normal or I would have to look at fixing it ?

It doesn't matter at all, it's just the expansion valve resonating like a reed instrument as the flow starts to open it. If you care you could try turning the spring upside down(Yeah, I don't know why but it works), or just tightening it or loosening it 0.2 bar or so, just to change it's musical characteristics.

Adjust the OPV while the sound is happening. Open ¼ turn and return to the same spot. Usually fixes it.

It does not bother me at all an even makes the brewing process kind of cool. As long as it not a sign that something needs fixing I can live with that.