Droning sound when car accelerates

we have an 03 camry Automatic, well maintained and having maybe 40K miles on it. Recently we have observed that when the car first accelerates from slow speeds it makes a low droning sound (drrrrrr).When it reaches higher speeds the droning sound disappears. We took the car for its regular servicing at which point we were told the center didn’t exactly know what was causing it but it MIGHT be the intake manifold. We took it to a Midas for a second opinion, and the guy there was not convinced it was the manifold and could not identify what might be causing the sound. Any ideas? have you come across this with other camrys orin your own car and what was the diagnosis? Much thanks for advice.

First look around all over the ourside of the car, and especially inside of wheel wells and underneath for something that might be loose like a splash shield or a piece of trim.

Does it change at all when you corner? If it does have the wheel bearings checked.

Is it any different when the car gets warmed up? If so, have the exhaust manifold checked.

Is there any kind of vibration associated with the sound, and does it change in charater with speed (other than disappearing at higher speeds) - e.g. does it sound like it speeds up or changes pitch as you go from say 10 - 30 mph? If so look over the tires for any kind of strange wear pattern.

Off the cuff, based on the description those are my first thoughts