I can't say what it is.
But you can rule out the individual pulleys like the tension pulley by getting some WD-40 or some 3 in 1 oil in a spray can with the straw. Carefully and sparingly spray the pulley between the belt and the motor. basically you are trying to lube the bearing.Don't get this stuff on your belt as it will degrade the belt, shorten it's life and leave gunk on your pulleys.
If you have lifter noise I recommend adding 1/2 a quart of Mystery oil to your engine oil. This has reduced lifter noise in many of my cars.