The Xbox 360 is famous (some would say, infamous) for the amount of noise it makes at all times, not least when reading discs. But what are these strange noises you may ask? Well, we shall attempt to shed some light on those.
At the time of its conception, the Xbox 360 was fairly ahead of its time. The technology used within the machine was, at the time, insanely powerful, and this meant it worked a lot harder than machinery of the same technical capabilities does nowadays, due to refineries in design of tech of the years.
To compensate for the heat generated by these hard working components, Microsoft has to incorporate equally as hard working fans into their console design to dissipate this heat and protect the core components and to avoid overheating. This design wasn't always successful, and many first day buyers reported problematic consoles and 'red rings of death'. But however you looked at it, those fans were NOISY.
Disc reading generates a certain amount of noise in all appliances, as the laser mechanisms insides needs to move back and forth to read data off of different parts of the disc at different times. It is nigh on impossible to eliminate noise when any kind of movement is involved. The Xbox does have an especially loud disc tray though, and this could possible be put down to slight design flaws on Microsoft's part.
Again, much like standard disc drives, hard discs need to read data from different parts of their internal discs at different times. Just because a game is playing off the disc, doesn't mean the hard drive isn't working hard to gather internal data from inside the machine on how to run it.
The fact that the Xbox is so noisy at doing this, and the PlayStation 3 is near on silent unless you press your ear to the console casing, could be to do with the equipments position amongst the other components. The PS3's hard drive is buried deep within the internal structure of the console, while the detachable hard drives of Xbox 360's are plonked on top for ease of access and use.
Installing your games to hard drive will eliminate noise from the disc drive, and much of the fan noise. This is because the game is being read solely from the hard drive, and thus, the disc drive doesn't need to do anything, and therefore the fans don't need to do anything to keep it cool, as it is not generating as much heat. You may still here a few reading clicks from the hard drive though, but this is perfectly normal.
If you have one of the newer, slimline Xbox 360's then you should notice less noise in general, as the console design has been updated from the original to take into account these grievances certain gamers had with the platform.
If it is still making abnormal amounts of noise and you are unsure, then take it to your nearest game shop for an inspection. You can be sure that they can tell you exactly what may be wrong with.