NewbeDoo

Hi, I have a MY03 WRX and have just had a quick shift fitted by the dealer, and have noticed an occasional 3Hz (approx) knocking which can be heard quite clearly, and felt through the gear leaver when at about 4K-5K rpm, I had the quick shift fitted at the 1000mile service interval, and hence have not noticed it previously (running in) The knocking only seems to occur in third gear, I mentioned it to the dealer but as it is only an occasional knocking I could not demonstrate it to him. Has anyone else had a similar experience and do you think it could be related to the quickshift installation?
Thanks for any feedback.
Tom