take the car back to the dealer who did the recall work. reason is they know what they took apart (the tech does rather) and they know what parts to look out for.
take the tech who worked on your car for a test drive. shit in manual land stay in the rpms a bit longer to rev up the engine . this may make the drone sound you describe. plus they will fix it at no cost (they should). going to a new dealer could be worse and possibly more repair time since they will have to troubleshoot work someone else did.
i had the recall done, and i now have a drone sound at a certain RPM under a load (say when going up an entrance ramp on a highway). when the car gets to a certain rpm, this drone sound is heard briefly as the rpm passes through. i have take my car back 3 times and the dealer cant "fix" the issue.
the tech stated it was the fan clutch that was loose and tightened it up. that helped a bit but the sound returned. the tech has to take a lot of things off (there's videos of the work being done on youtube) and its just like taking apart something at home, only to put it back together and realize you have one screw left that you don't know where it goes to!
i think i feel /hear this vibration more over by the muffler area. i have been too lazy and have had other things to do and have not been back to have this looked at again. its annoying to me because my car did not have this sound but its more annoying to go up there, be put in a rental and have the car torn down and looked over again as my time is much too valuable for me to go and have this done. i will have it looked at on my next oil change interval when i have to go up there anyway.
sorry this is long and this may not be what you are noticing on your ride, but i thought it worth tht e time to type this to see if you may be hearing the same thing.
i will say i don't have any loss of power or other things. the car is as spiffy as ever.