Squeaky audio tapes are typically caused by the binder (or glue) of the tape "leaking" from under the top layer of the tape--the layer that makes contact with the deck's heads. As this leakage occurs, the binder begins to absorb atmospheric moisture. Over time, the binder can stick slightly to the tape deck heads. Although it's unlikely that this will cause head damage, it can still be quite annoying, especially when listening to quieter passages. Over time, the tape will end up sticking to the tape rollers and heads, probably causing the destruction of the tape. As with many issues of this type, there is a tried-and-true DIY solution. Applying a little heat for a short amount of time can solve the squeaky menace.
Preheat the oven to 54.4 degrees Celsius. Set a digital timer to eight hours. Rewind the tape fully in the deck, VCR, or reel-to-reel, depending on the tape type.
Cover a metal baking tray in aluminium foil, shiny side down. Place the tape on the sheet.
Allow the tape to "bake" for six to eight hours or overnight. Allow the tape to cool for one hour. Immediately make a copy of the tape before the binder can reabsorb moisture (within 48 hours). It is not advisable to use the tape again after it absorbs moisture, since it is impossible to predict when the tap will bind to the heads and self-destruct. As a result, it is advisable to use the copy and retain the original for archival purposes only.
In most cases, tapes cannot be "baked" more than twice.
Make sure the baking environment is properly ventilated, as the plastic will outgas slightly during baking.