After much debate i finally bought some campagnolo Neutrons today, treated them to a new cassette (105 11-28T as per previous wheel). just fitted cassette and put wheels on but it seems to be really rough and almost grinding when turning the pedals. Tried adjusting gears but no difference, dont really want to ride on them through fear of causing some damage.

Could it be that i have done something wrong when installing the cassette?

Old chain?

No, its on a Trek emonda which i only bought in January this year, im hoping its not a dodgy hub

How much use has the bike had? Almost 6 months and that is plenty long enough for a chain to be worn enough to not sound good. Everything is installed properly and not overly tight?

Try old wheels with new cassette or new wheels with old cassette, narrow it down, process of elimination init.

Just been looking on the net and wondering if i tightened the cassette enough, it said you are supposed to keep tightening until you hear or feel three or four distinct clicks, i just did it tight as was concerned about over tightening. ill have a go early doors tomorrow and see if that sorts it