I purchased the STZ driver online in late Aug 21. It worked well for some time. After using it for about 2 weeks, the driver's head came loose and rattled for some unknown reason and I tightened it. Since then, it does not seem to perform as well as when I first received it since my driving distances (per Trackman) are lower. I wrote to Mizuno through their website but had not received even an acknowledgment. Appreciate any advice as to what I should do about it. I have been playing with Mizuno clubs ever since I took up the game some 30 years ago and never had any issue until now. Thanks