I had a manual Rover 623 for a while, it was super refined even up to the redline. Is the exhaust blowing a wee bit or is it the nature of the auto box?
It could be both of those as I think there is a tiny blow somewhere. It also sounds a bit tappy which doesn't help, and my old 416GTi was the same albeit much worse (sounded like a bloody sewing machine). I had the valve clearances done on that with zero improvement. phil_lihp's 2.3 Accord sounded much quieter when I drove that on the collection mission.
Like I say it's a minor thing, as it's still a great engine for cruising along at 70 for long periods.