What is the major source of engine noise for non-propeller aircraft? Sparked by this question:

Take any non-propeller powered aircraft, when idle, the sound produced by the engines are fairly low pitched, and as the engine spins up, increasing in pitch before becoming a full on roar.

I figured that the major sources of engine noise could be 


The air rushing out of the exhaust,
The noise of combustion in the engine, 
The mechanical noise of engine parts


My question is what causes the majority of the engine noise at idle vs full power.

To stop this question being too broad, lets discount noise coming from any source that's not the engine's of the aircraft in question. I just want to know about engine noise.

I had a look at this question, but that doesn't have any information about the source of engine noise, just that the turbine itself will also produce noise which is something I didn't consider.
At full power it is the mixing process of the fast exhaust flow with the surrounding air. Note that noise increases with the sixth to eighth power of jet velocity, so the loudest engines are those with a low bypass ratio  and reheat on.


Diagram from a Stanford web page on noise. The jet velocity is in ft/s.

At idle the biggest noise source of the whole aircraft is the flow around the lowered landing gear, gear cavities and the slotted flaps that you asked us to disregard. The engine noise is a combination of intake noise, bearing noise and nozzle noise, and which of those contributes most to the engine noise depends on the individual engine and its installation into the aircraft.