The loud whistling and popping has to do with the equipment that the person monitoring the frequency is using in addition to the range they are from the airport.
Depending on local law you could purchase a receiver capable of receiving those frequencies yourself directly. Under some conditions however transmissions may sound like that because they are AM and subject to whatever interference is on the air at the time.
When you are in an aircraft you are subject to less interference because there are no objects between you and the transmitter. The frequencies you need to be able to receive are 118.000 Mhz to 136.975 Mhz AM mode for civil aviation.
Even if you are not directly near a major airport there is likely controlled airspace near you that you can check by looking at a sectional for your area. That will have the frequencies in use by your local airports. Then you can listen to controllers with your local accent. Once you know the words you'll be able to pick them out of the LiveATC feed better.