[1000mp] Still struggling with my AGC problem

[PA5CA Frans]

I'm still struggling with my FT1000MP mark V Field and the AGC.
Did some more tests and found the following. perhaps someone recognizes this
phenomenon.
My initial feeling was that RF came in to the receiver and therefore the AGC
came on.
But had a little more time to spend.
Did the following.
- I directly connected a antenna to the RX (external input) input.
  Made TX (SSB) and noticed the same behaviour, As soon you release the PTT
the S-meter comes from S9 and
 gradually it settles S0, time approx 2 seconds. (AGC setting Auto or slow),
switching to fast or AGC off makes a
 difference, mainly it goes to S0 spot on. (Sub receiver shows exact the
same)
 So I thought perhaps an RF power change may show different, but that became
an illusion. There is no difference in
 behaviour between 3 Watt or max 95 Watt.
- So I tried different modes. AM, FM okay. AGC seems to responds normal.
  RTTY. here I see some AGC behaviour.
  So the next was, it may sound odd but I loop back the monitor audio in to
the microphone (give that nice high tone)
  and noticed that the pitch makes the AGC vary in behaviour.
  Lower the pitch (tone) causes more AGC behaviour after releasing the PTT.
  I tried this several times and I'm almost certain that the pitch influence
the AGC behaviour!
- So the problem occurs in SSB (LSB/USB) mode.
- There is no relation with the TX RF output power.
- But tone pitch has impact on the AGC behaviour.

RX sensitivity looks normal.
ALC behaviour for what I can observe seems to be normal.
The radio shows no abnormalities except for the AGC behaviour while
releasing the PTT.
So could the ALC causing the above phenomenon??

So help or hints are most appreciated on this mater. It drives me
crazy.....#$%*(&^$))(*%

best 73,
Looking forward to some replies.

Frans (pa5ca)