phantom power

It's very unlikely that voltage fluctuations in the phantom power (PP) could cause hiss.

There are three pins. Phantom power is connected to both pin 2 and pin 3 (but as long as your cable is not broken, simply use it).

X stands for ground (it is connected to the cable shield).

Pin 1 (X) = ground
Pin 2 (L) = + most commonly, or Left
Pin 3 (R) = - most commonly, or Right

The risk is higher if it is an unbalanced connection. The Sound Reinforcement Handbook by Yamaha says something like this:

"In a phantom power system, the polarizing supply voltage is placed on both of the signal lines in a balanced connection, with the same polarity on each line. Dynamic microphones connected in a balanced system with a phantom power input are then protected from damage, theoretically, since the system results in a net zero DC potential across the coil. However, a dynamic mic connected unbalanced to a phantom power input may be destroyed."

In other words if you take a sm57 and plug it into a phantom powered mic pre using a normal balanced mic cable then you should be safe.

If you take an unbalanced mic and wire it with a xlr plug so you can connect it to that same input then you could fry the mic. In a balanced connection the 48 volts is running parallel down the 2 signal wires. With an unbalanced connection (2 conductors) you have 1 signal wire and ground and doing this is basically completing a circuit that sends 48volts directly to the mics voice coil.

So the steps when connecting are:

1. Turn down those master faders.
2. Plug in mic.
3. Turn Phantom Power on.

and when disconnecting:

1. Turn down those master faders.
2. Turn Phantom Power off.
3. Unplug mic.