Well it's an 08 WRX I was getting the -5.6 in 4th gear at around 3k rpm. There's an accessport, exhaus,t the boost is turned up a little, 38 mm wastegate. That's pretty much it. I'll have to get the logs off of it and upload it.Very hard for us to answer this question. It could be a number of things. We need a lot more information to be able to help. Like driving condition, gear, rpms the knock occurred, up hill/down hill, what kind of car it even is, what all modifications are done to it. And even with these things it will be hard to pinpoint the cause. Best bet it to upload a log for us to take a look at.
I'll email them and see what's going on.You may have already, But I would also Email Cobb Support. They respond very quickly. (Via email) I send in Datalogs and they look at them for discrepancies or explain questions you may have.