[Help] MHZS CD33 Clipping

Hi everyone,
  
I hv been using the CD33 for more than 1 year. I hv not modded the CDP, only changed a GE 5670 tube.

However, CD33 sound strange these days. After turning it on and playing for 15minutes, the output starts to clips, with the noise of" se le sa la" or so called 沙石聲. When i paused it, that sound went off.

Can anybody Help me? Have bothers here encountered the same problem?
Thx very much

Will it be the problem of the clock? thx everyone

try to replace the tube 6n3 back, if the result is fine.
that is the ge5670 is over.