A landing booster creates < 10% of the noise of a rocket launch. This is possibly reduced much further in near vacuum conditions (Moon/Mars). No sound suppression could be fine at these noise levels.
To expand on the previous answer;
A rocket's engines must create more force than the force of gravity on the rocket in order for it to accelerate skyward (when taking off this would increase its velocity and when landing this would decrease its velocity).
Therefore, the thrust-to-weight ratio of a rocket is a key metric in its performance. At launch, this ratio was 1.5 for the Space Shuttle while the Saturn V was at less than 1.2, resulting in a very slow takeoff.
As the rocket exhaust gasses create both the thrust and the damaging sound waves, the sound created by a rocket is roughly proportional to its weight for any given acceleration. Assuming the acceleration of a landing booster or spaceship is equal to that of one taking off, we can say the sound created in either scenario is (very roughly) proportional to the rocket weight.
For the Falcon 9, a completely empty booster is given by Wikipedia as weighing 22 Metric Tonnes, while a fully loaded stack is over 549 Metric Tonnes. Therefore, only ~4% of the takeoff sound is generated during landing if the booster was using its last drop of fuel to land. This is backed up by the landing boosters using just 1 of 9 engines (presumably throttled down).
The problem would be increased slightly during a landing if there is no flame trench (landing on a flat surface will reflect more of the sound upward toward the rocket engines) but this is still too little to require active sound suppression for the Falcon 9.
As for sound suppression in vacuum or near vacuum conditions, the answer to Does a rocket sound louder to the astronauts as it leaves the atmosphere? indicates that sound would be much less of a problem on the Moon or Mars due to the exhaust gasses being able to flow away from the rocket without the interference of external air. The exhaust gases from a rocket engine are much less dense than air at sea level and rapid compression an expansion of them occurs after leaving the rocket (see https://en.wikipedia.org/wiki/Shock_diamond). The above answer indicates the shock-waves created by this are responsible for most of the sound, a problem not encountered in vacuum.