This fix is for a 25" Sanyo that May (Or May NOT) be related to your
model. Maybe it wil be in the ballpark enough to fix yours.

Q: Audio distortion then muting at higher volume level OR Volume level
fluctuates up & down. Sound could be brought in via adjusting slug of
T131. However, adjustment range was narrow and degraded later.
A: Replace T131 Sound discriminator coil. (ST 181 S 6HC)