By your description it seems that it is a bearing in one of yours engine accessories, like the subjected Generator, but it can also come from the waterpump,
AC-compressor, servopump, or the thermoclutch on the fan if the car is equipped with that, but most common is that it is the generator.
How to find out? With the engine off, try to feel if you can feel any radial movement when you grab the accessories pulleys and (shake) them. Due to the belt tension is it often hard to feel any fault in this manor.
An alternative is to loosen the belts and try then, but it is better to first try this:
With the engine running, grab the biggest screwdriver you have, hold the handle to your ear, and put the tip of the screwdriver, on the suspected parts housing, beware of moving parts.
If it is a bad bearing it should be like a grinding sound compared with others.
There is a special tool for this instead of the screwdriver, and that is similar to a doctor’s stethoscope and is of course better than the screwdriver, but not too many have such a tool in their garage.
It would be best if it was the generator, cheapest and fastest to fix.