Issue when changing sequence

I have an odd issue, I have 3 sequences, nothing too complicated, but when I switch from sequence 2 to either 1 or 3 there's a weird bright sound at the beginning of the loop, this is not from any of the samples in the tracks or from the synth.
Another thing I noticed is that when I switch, on the diagram where it indicates which track is playing (top right of the screen) all tracks flash briefly.

Any idea what this could be?

Note, when I switch from sequence 1 to 2 or 3, all is fine, this happens only when switching from 2 to 1 or 3.

did you try to mute every track in the first sequence also?
did you do any cut/copy/paste from the sequences having some strong swing on?