Usually quiet noisy.
Most RVs are designed for convenience and aesthetics but rarely for noise control. There are small moving parts through out the RV that rattle when the RV moves especially on rough roads.
If this is an important factor for you then you should either test drive your RV before your rental trip or request the RV owner to send a recording of noise when RV is moving.
Perhaps this is not a show stopper issue, but please factor this in so that it does not come as a surprise when you begin your rental RV trip.