Advice / info please. I was out last night driving down some nice roads. I noticed when driving hard and changing gear, I felt a slight hammering from the gearbox or diff or something. Any clues? The noise was apparent in second and third as I let the clutch out.

Regards Peter

Sounds like wheel hop to me. Old school draggers call it axle tramp, it's your rear wheels "hopping" due to the sudden unloading of torque. In many cars set up for handling, the rear sway bar is "pre-loaded", helping to dial out some of the car's tendency to push through corners. This pre-load does introduce wheel hop in many cases. The Cadillac CTS-V is a perfect example.

I'd recommend a little more clutch slip on your hard, high RPM shifts. Or if you don't care about handling, just straight line acceleration, put a softer rear sway bar and springs on.