Well, this is kind of embarrassing. I took the car to Melvyn's garage on Monday and was told all was well. I think a mixture of new car paranoia and the unique way Morgan sound proof their cars (ie none) had me worried!
Anyway, since then I've been out and the noise is hardly noticeable (strange how the mind plays tricks). I can now continue falling in love with this amazing car again!
Thanks for all your assistance.