HKS Mid Pipe Problem

[JB-370z]

So I got the hks exhaust installed a few weeks back and I am having a weird sound coming from my mid pipe! Its like a high pitched rattle. The shop put it on the lift and its comming from the mid pipe and not somthing else. Waiting on HKS to open monday! I also have berk high flow cats, does this make any difference?? Does anyone else have this ugly sound? I can really hear it the faster I go and it is mainly while the rpms are going down instead of up. They said they have never heard a sound like this in a mid pipe. What is in the mid pipe? I am going to record this sound and also send to HKS. Had a turbo hks rsx type s and none of there parts have ever failed till now, but it mught be somthing else!