It actually sounds OK around 7k and above!!
Glad to hear it - it sings, doesn't it? I wish many other other boxer riders would realise how to get the best out of their tractors

It actually sounds OK around 7k and above!!

is that bog standard gl5?Get a service kit online from Motorworks or James Sherlock and just use a good quality engine oil available from any factor. My tip would be to change the gearbox and drive oil at the same time so you know everything is fresh. Easy job which takes 10 minutes and a litre of GL5 will do the job nicely. I do this every service and 120,000 miles later she runs like a dream.
The clatter on start up is normal and I wouldn't worry about it. I'd keep the revs up a bit and you will find the bike is smooth and responsive.
I used 70-140 syntrax on my last gear-lever oil change.