The atty gets warm because the coils heat up and retain heat, if vaping continuously she'll tend to heat up more. When I had over heating problems on my rba's, it usually was because I had to much wick and was retaining heat. Also if not getting enough air to cool down the coil, it can get warm.
If a battery warms up then one is having a problem, either the ohms are to low and demanding more amps than the battery can deliver, or getting a short in the coil, which drops the ohms, and doing the same thing. If you feel the switch getting warm or suspect the battery heating up, stop vaping, unscrew the switch housing and check the battery, if warm, check our coil. Know on the PT 2 and 1, if you over tighten the atty to the mod, it can twist or break the coil wire and create a short or a hot spot.
If you don't already have one, a atomizer ohm meter is a must have tool for mechanical users. With a PT it's not as critical as with a rba or rda, but, if you thinks something is wrong it's good to be able to check your ohms, plus if you do get an rba, then you will have a way to check you ohms so that you will know if the battery you are using can handle the build.
The whistling you are hearing is the air going through the atomizer, which is supplied through the stem on a pt 2, not familiar with the 3, but think it's the same way. Make sure you don't over tighten it, can tighten the air up to much and promote flooding when taking a draw, and mess up your coil.
