Mine does it too or did until I messed around a little bit. I took some of the filler from an empty cart, have a few since I did the ptb mod. Any way I took a little bit of it and rolled it up between my thumb and index finger and stuffed it around the base of the atty where it screws into the battery pushed it down with a pair of tweezers and it seems to have helped so far. Try a few different thickness till it stops the whistling. also the atty needs to be tight for this to work. It hasn't affected the draw at all and was the only thing I could think of to stop the noise. It did seem to get some juice on it after a few tanks but it didn't make a difference with performance and I just make a new one and change it. I hope this works for you like it did me.
Good luck and happy vaping!