Just picked 4x up- 6mm - 7mm tread £45 for all 4! Bargain I hope!!

Got all 4 Goodyear wrangler HP’s balanced up & fitted earlier- car is noticeably smoother & handles better but that 30 mph whine is still there.
I’m thinking it’s 3rd gear on the auto box?

Any suggestions?

Booking it in for all 4 wheel alignment this week to save my new tyres from getting chewed up!

It's a cost/benefit thing. It may be be difficult and expensive to track down this whine, for little actual benefit. It's your call.

Monitor it and turn up the radio! If you can't live with it, then investigate further.

Yep - you should be in 4th at 30, try using the manual mode on the gearbox to see if it is gear specific.