Accuracy

[bradaz11]

put some tape over the end of the mod, and see if bullet exiting is in centre, and making a nice round hole

[Stigg]

As mentioned, likely baffle strike - if the muzzle has been cut slightly out, or to the outside of the barrel rather than the internal barrel then it could be the cause - you don't see it on the flash hider because the crown is wide open, whereas decent moderators have very small holes farther out from the barrel crown.

I had this on my Sako P94s, it only became apparent when I changed mod to one with a smaller exit - had to get the thread re-cut concentrically to the bore.

I think that is the case so will leave it for now as it's not that loud anyway being a 22lr!