It was a brief affair, but I am afraid I am returning the amp to the shop today.
From all I have read, the tweeter sound I am experiencing is normal and expected of these amplifiers, which regretfully makes the amp completely unsuitable for me. Primarily was to be used as a home practice amp and a studio recording amp, and with the hiss of that non-adjustable tweeter it would be no good for either of these uses. Would be no problem at all if it was to be used as a gigging amp. I know the issue could easily be helped by sticking a bit of foam or felt over the tweeter to block out the white noise, however whilst I may be happy to do this with a second hand amplifier, I don't feel like I should have to do this with an Amp I have just bought brand new. If it's not perfect for me, it needs to go back. I have requested that the shop look into the return as a fault as well as being not fit for purpose, as I really don't think a tweeter should be that loud. Perhaps at 25 my hearing is still better than others and it's just more audible to me, who knows.
Otherwise, the amp sounded good and I am sure it performs well for 99% of the bassists out there Lesson learned: listen harder when trying amplifiers out before you buy. (needless to say I did not try this exact amp before buying it, perils of online purchasing..)
Anyway, apologies for the thread hijack!