GB on Ipad3: How can I change the volume within one note?

Hello,

Just started my 1st project in the new GB 1.2 on Ipad3. I started with some strings which I recorded by rubbing the chords. After editing and moving the notes seperately, I still have some strange volume changes in my piece. At some places the volume suddenly droppes down for a very short time, creating some sort of 'whoop' sound, and after that the sound decreases for a few seconds and is suddenly loud again.

If I copy these bars to another track, the volume issues are exactly the same. I can change the volume for one note by pressing it and choosing the 4th button (have a Dutch version, don't know the Engelish word for it), but these values are all looking normal. Also, when I change the volume of one note, it doesn't effect or solve my volume issues at all.

Anyone familiar with this? :L

Thanks!

PS: What if the volume is right, how can I increase the volume of one note? Can it be changed after playing it?