Start quickly? Shift smoothly?

You may have a brake caliper dragging (look for excessive brake dust on a wheel) or a loose or broken heat shield on the exhaust (they can make a racket). Just a starting place of common noise generators on a car. The heat shield would have no bearing on increased mileage (brakes might if not working properly).

when accelerating , say a knock, then goes away, could very well be engine knock. Hard to diagnose here.. I'd get it checked out.

noisy on acceleration. But it seems fine otherwise and gets 60 mpg. We have had 6 Hyundai vehicles- Sonata, Elantras, and an Ioniq hybrid. Loved all of them; never have had a problem. My old hybrid did not make this noise; though, the new one does. I have not had it checked out - it’s a year old now and no other issues besides a noise that doesn’t seem to affect performance.
Your guess is as good as mine!

passenger cabin --- intermittently. I took it to four repair shops and none could determine the source. Determining the source could have probably required taking the dashboard apart so that was likely in the way of finding the cause of the leak.

On a day when it wasn't leaking, I took it to the dealer and traded it in.

If a mount is broken the engine can torque and lift, possibly opening the manifold causing the increased noise. I had it happen in a Chevy but in my case it pulled the accelerator to the floor while simultaneously ripping out the power steering and brake hose. Nearly got me killed. Just a guess, Im no master mechanic.