A stealthy diesel-electric sub?
Yup. With the diesel off and running on battery power they can be very quiet.
Nuclear is not magic. In fact, at anything above very low reactor power, circulating pumps in nuclear subs make detectable amounts of noise. They are built to work on natural convection at low power, but need forced circulation at anything higher. The technology gets better every year, but batteries are just completely silent.
The real advantage nukes have is that they don't have to surface for very long periods of time.
Their are so many other ICE's ( many you could say fall into the inventor engine arena ) to add to the "-electric" IMHO that can burn diesel that would be so much quieter. Unless they have ways of masking diesel engine noise that falls into the category of "don't ask what I do for a living"...