Presence of a tone during silence part

with 04440bc5 and P7c3a-stereo_-dtx_24400_48.zip

we can here a tone when one channel is silenced

in the figure below, from top to bottom

• element_brate
• right channel float
• right channel fixed-point
• spectrum (bleu is float, purple is fixed point)

The second figure is the same as the first one, but with only temporal signals. Similar issue happens on the left channel as well. This problem seems related to #854 (closed), where the tone was reduce and no more audible on active content. but it seems that more is needed during silence