What happens if your laptop keeps making strange noises because every so often very loudly it makes the sound of a door opening as well as another weird sound is there a backdoor Trojan on it

If the sound is coming from your speakers then it is definitely some program operating without your knowledge. If you mute the sound and it still makes that noise then there is something wrong with your hardware. Without hearing the sound it is hard to tell, but the parts most likely to make noise are the hard drive, the CPU fan, and the DVD drive.