I recently had an oil change and 30,000 mile service at a Honda dealer. Car was running perfectly when I took it in, but now infrequently ‘moans’. The low moan usually happens after I have driven the car for awhile, at a stop sign and I slowly accelerate to take off. In SF, there are lots of stop signs! As soon as I accelerate to full speed, the noise stops. Can happen as often as five times in ten mins or not at all if I am only driving on the flat. Have had it back to the dealership numerous times since, test driven it three times with them and only heard the noise once (with a technician). They cannot find a reason for it and seem to have given up. The car is a 2009, has 16477 miles on it and is under a Honda Care warranty. I purchased the car in 2012 as a preowned certified Honda and have had no problems with it and as I only drive about 3000 miles a year have had no previous services or maintenance issues.
Check to see the air filter is installed correctly and that all clips and hardware that hold the air cleaner in place and seal it from air leaks are secure.
Can you stop and restart the moan by lifting on the throttle and reapplying?