Yeah, first thing I'd do on the apollo is take off the top, and use a paper towel to sop up any juice that's collected around that seal on top of core, and on underside of top cap. When I get funny hits, 90% of the time that takes care of it. You might want to give the core a little light twist to make sure its all the way screwed into the base. I'd also change the drip tip, since I've noticed that some of mine amplify the noises the cartos make, and some sort of muffle it. Ceramic and plastic seem to be the best 'mufflers' and some shapes work better than others, too. But, I'll also say that I go thru stages when cartos are very loud (whistle is the worst, by far, but I get a lot of gurgling etc also) and then they calm down. That's not your kind specifically, but just something I've run into with a bunch of different cartos. Grandes were always loud and obnoxious and horrible for me. I haven't had any issues with the Apollo making noise at all, though it does gurgle a bit, but no whistling at all. Last but not least, if it really bothers you, just syringe out the juice, and rinse the tank and caps... unscrew the core, and really make sure the core is seated in there properly when you screw it back. I know the few people who have had issues its turned out that it was just assembled quickly, and when they take it apart and put it together carefully, its all resolved. I've NOT heard about the whistling thing though. You might also want to ask here...
http://www.e-cigarette-forum.com/forum/tanks/305367-reviv-e2-apollo-tank-dv-4.html#post6558902 and perhaps someone else will have run into the same issue?
