Humming sound when I accelerate?

Just got my catalytic converters cleaned out expensive too, but (I had a P0420 code) and that’s what they recommended. However, I thought that would fix the humming sound, but it didn’t. I’m not sure what this could be. The sound isn’t loud, but it is noticeable. Nonetheless it only does this when I accelerate. I read it could be when bearings but I’m no mechanic.