Big strange sound from the engine

[yazmo]

hello last night i was about to come back from work and my engine was making a very different rev sound i can't describe it here but it'slook like it was struggle.

after 10 minof driving i decide to put some gas cuz my tank was mostly empty,while driving back to home i decide to raise the rpm over 4000 and the sound was gone.

anyone know if this a sign of something

[ericem]

Maybe the idler a pulley? Time for new belts? A/C on or off?

[yazmo]

pulley have just been change 40000 km ago and a/c was not on.the problem is gone just hope it will not come back