Is your recording crackling when you transfer it from the OP-1 via USB to a computer? This will tell you if you have a problem only on the D/A of the OP-1 itself, or an overall problem.
Mine doesn’t crackle per se, but I definitely have to be careful with some of the synth’s levels, especially the more digitally modelled ones.
I fully agree with Poonti. Maybe you have increased in the Master EQ section the frequency too much, that could easily lead to crackling. ycheck also the recording input level, if its too hot, it causes crackling too. The OP1 is a bit Diva when it comes to too much volume. Check the settings…also maybe you drive an effect too hot…results also in cracklinghousen.