Philips 28CL6770/25Z intermittent loud audio distortion

[JamesQB]

Model Number: 28CL6770/25Z
Chassis: FL1.10AA


Hi

For some reason, even with normal volume level, this set intermittently booms out a second or three's worth of loud distorted sound, but (mainly, although has done twice during programmes) only during commerical breaks! The kind of crackly ear-splitting sound that you get from over-amplification or a blown speaker.

Using Sky digibox RF output for signal, incidentally.

Any idea what's happening and what the cure may be?

Thanks,
James

p.s. I have schematics if anyone wants them.

[JamesQB]

Problem traced to Nicam board. Needs replacement board.