Distortion (digital distortion sound) from L1 tower

Vocals on my L1 used to be pristine and clear, but now distortion (digital distortion sound) from L1 tower intermittently at the transient point when a person sings. It happens only with vocal signals and not with instruments. All levels are properly set. The "green/red" signal light on the L1 base stays green when distortion sound occurs. Any on else experience this? Any suggestion of what the problems is?

 

I am using a Bose T8S Tonematch mixing board with very little effect other than a small amount of reverb.  

 

Thanks.

Yes, I experience the same.

 

I assume you tried different channel, mic and cord in order to eliminate the basics.