Pawel, the sound you hear is the g-forces acting on the diaphram inside the carb-the engine kind of pauses for a milisecond and then resumes as normal, mine did this too. I found with a little more time and a slight adjustment of the low needle, this has dissapeared. Mine would do it if I would be on a 45* downline and then pop into a wall very rapidly as you mentioned.

On the oil for breakin, I use only Pennzoil aircooled @32:1 and I will stay at 32:1 for the rest of my engines life. I have two Zenoahs that I run too and they use the 32:1 as well so I only have to tote one fuel jug to the field. My nephew switched from Pennz 50:1 back to 32:1 on a converted Homelite 33cc and picked up a noticeable power increase.