V70 II 2.4 Gasoline comp. with diesel; noise level in the interior

Hello together, I’m planning to buy a Volvo V70 II soon and I’m not sure yet about the engine. I’m reading now across the posts that’s all very helpful.. just not about the noise in the interior. I want to be able to ride the car comfortably 160 km/h on the highway with rather quiet noise. Low speeds would certainly be helpful. I drive about 18,000km a year. A lot of highway but also city. For economic reasons would be a 2.4 with subsequent LPG retrofitting my choice. I just wonder if this makes me “acoustically” happy. What do the other drivers of this model say. Will it be loud at the higher speeds? For 5 years I have been driving a 1.8l Audi A6 of 97. It just turns too high in the speeds and annoys me acoustically. Talks with the children behind are quite exhausting and loud… Or should I use a diesel at a limit of about 8000 instead? the manual transmission): 2.4 l from 2003 with 130,000km you could probably get for approx. 5000,- plus 2000,- LPG. a D5 from 2001 under 180000km could also start from 7500,- would probably be smoother but expensive in maintenance. what do you think? How is the noise in the interior at 160 zw. the 2,4l petrol and a 2,4l D or D5? Thank you for your advice first.