We have not used your cabin but we did go on this ship earlier in the year on the deck below yours. It is the first time we have ever been that low (we were midships) and had the same concern as yourselves. However, we were amazed at how quiet the cabin was - no engine noise at all and only minimal noise from the air-conditioning system. Hope this info helps.
Yes we were also on deck 3 midships and found it very quiet and comfortable. This was around south america for 7 weeks and loved every minute of it. Ship, staff, food everything. Look forward to going on her again.