What is the root cause for TD-SCDMA audio noise burst?

In TD-SCDMA telecomm, the phone sometimes output audio noise burst, that last about mille-second duration. It always happpens at almost the fixed time after the phone boots up. And the audio noise pattern is almost the same.

What is the root cause for that?
Is it because of the heat of the circuit?
Or spurs in the audio?
Or out-of-frame in telecomm?

for GSM or TD-SCDMA, if caused by out-of-frame, the issue may be interrupted at second level.
Now my issue is at mille-second, so I guess it is caused by phase-hop of the VCO. Right?