The squealing on cassettes is caused when the lubricant in the tape evaporates or rubs off from excessive use. When there is little to no lubricant on the tape, it causes a high pitch wailing noise when played. (Sort of like a kettle) It's very annoying, so I will teach you how to fix this problem easily.
Step 1: What you will need
&Bull;A squealing cassette
&Bull;A portable cassette player (particularly one that opens while you're playing the tape)
&Bull;A clean cloth
&Bull;A cup (optional)