strange noise after some recent work

[majidmo]

Hi guys,
I need help with a new problem. X5 is 2003 3.0 and has 109 K miles on it. I recently changed tires, brakes, Thermostat, drive belts A/C and Alternator belt and valve cover gasket and had a 4-Wheel alignment done (most of them at the dealer). After that I noticed a strange sound while driving (listen to attachment). It starts when I take my feet off of gas pedal and appears it goes away as soon as I press gas pedal. No vibration. I don't hear it while car is idling.

Any idea what it is or where to start?

Thanks in advance.