Volvo FM Driver's Handbook Manual page 713

Using the Cassette Player 27
Note: Do not release the AUD button
before "CLN RST" is displayed to reset
the clean condition.
If you experience poor sound quality
from your cassette player, try playing a
different cassette tape to see if the tape
or tape player is at fault. If the second
cassette tape also has poor sound quality,
try cleaning the tape player, regardless
of when the player was last cleaned.
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