Why does My iPhone give me a buzzing noise?

Hi! I am here cause I am freaking out right now and I'm sure someone here can help me out. So I got a new Iphone 4 a few months back but it's still like brand new. And then one day a huge incident happened so I had to give it to a store and they pasted this Plastic-ish glass thing on top, like a screen protector but a hard one. The real incident was that my lil bro dropped my phone and something in the phone changed but anyways it was like the first time I dropped it and it already got damaged and I wasn't pleased but after buying this screen protector thing everything was back to normal and I bymistakenly dropped my phone a few days ago and I freaked out but like nothing happened thanks to the protector. So the real prob, When I record a video on my iphone camera, and then open the gallery and watch the video, it makes no noise except this buzzing noise. The buzzing noise is like high-pitched btw. So the reason I freaked out is that i dint like this happening to my new iphone. And I hope its not something big to repair but like I saw on this website that it can be because of any screen protector/case and I checked my phone (can't believe I was this stupid) and In a minute I ripped off the screen protector:( And then I checked it again, I mean I recorded a video and it was still the same thing (Stupid idiotic website). I tried blowing on the hole stuff and all but technically I am not a genuis and I assume that most of the answers are to remove the parts of the iphone and reasemble or something but I really can not do that cause I'll end up making it worse. Any way I can fix this? And fiy this problem dint exist before and it is not because my brother dropped the phone, but most importantly it is really hard to protect this phone from my little brother and now that the screen protector is off, I need a solution quick and then I need to put on another accurate screen protector. Please help. xxx