So assuming it is from the outside of the cabin, as you might hear it louder than you do with windows open...I would guess its the brakes/rotors. Did they replace the rotors or resurface? It can be something rubbing up against the rotor when the car is moving.

Another thing you should try is to drive in an alley way that has walls on both sides, and listen for the noise as you drive down slowly. I can locate the sound of things much better when road noises are buffered.

On other cars, I have replaced my brake pads before and had some noises come from not inspecting forgot to use the brake quiet.

 

A little early in your case, but take a look at the heat shields over the exhaust system. The aluminium shield material corrodes around the non-aluminum fasteners and the shield either becomes loose enough to rattle against something or falls off entirely.... possibly rattling against the exhaust components if it does not fully depart the vehicle. Three of the shields on my 2011 HL became loose (and two eventually fell off) at around the 60K to 70K mile point. They can make quite a racket.

Paul

 

Thank you all for responding. Last week the noise completely disappeared irrespective of the kind of road surface I was on. I highly suspect it was a loose heat shield, which subsequently broke off a few days ago (I heard something clatter drop while driving).

I will have it checked out at next scheduled service in March when they swap over to summer tyres. For now, no noise is good news.

 

Spheric2, I would also check the disc brake metal shield on the back-side of the rotor to make sure its not bent/loose while the rear tire was removed/mounted. Another place I would check (a long shot) is the spare tire to see if its securely mounted...