Are the following sentences natural to a native ear?
1. Who are you lunching with?
2. It sounds like it is day and night
1. Who are you lunching with? This is grammatically correct, but in AmE, lunch is rarely heard as a noun. More natural would be "Who are you having lunch with?" It may be different in BrE.
This would be acceptable in BrE, though I suspect that 'having lunch' would be more likely to be heard.