Annoying beep with A400P on PSTN

CPU0       CPU1
  0:    2060576          0    IO-APIC-edge  timer
  1:          9          0    IO-APIC-edge  i8042
  8:          1          0    IO-APIC-edge  rtc
  9:          0          0   IO-APIC-level  acpi
 12:          4          0    IO-APIC-edge  i8042
 14:       6256      13538    IO-APIC-edge  ide0
 15:      17980          0    IO-APIC-edge  ide1
185:       1156     142853   IO-APIC-level  ehci_hcd:usb1, uhci_hcd:usb4, sata_via
193:          0          0   IO-APIC-level  uhci_hcd:usb2
201:          0          0   IO-APIC-level  uhci_hcd:usb3
209:         35      79036   IO-APIC-level  uhci_hcd:usb5, eth0
217:    2017730          0   IO-APIC-level  wctdm
225:    2005040          0   IO-APIC-level  b4xxp
NMI:          0          0
LOC:    1994893    1994900
ERR:          0
MIS:          0

$dmesg | grep dadhi
dahdi: Telephony Interface Registered on major 196dahdi: Version: 2.5.0.1
dahdi_transcode: Loaded.
dahdi_echocan_mg2: Registered echo canceler 'MG2'

$cat /etc/asterisk/chan_dahdi.conf
;
; DAHDI telephony
;
; Configuration file

[trunkgroups]

[channels]

language=en
context=from-pstn
;context=from-zaptel
signalling=fxs_ks
rxwink=300              ; Atlas seems to use long (250ms) winks
;
; Whether or not to do distinctive ring detection on FXO lines
;
;usedistinctiveringdetection=yes

usecallerid=yes
hidecallerid=no
callwaiting=yes
usecallingpres=yes
callwaitingcallerid=yes
threewaycalling=yes
transfer=yes
cancallforward=yes
callreturn=yes
;echocancel=yes
;
; Some DAHDI echo cancellers (software and hardware) support adjustable
; parameters; these parameters can be supplied as additional options to
; the 'echocancel' setting. Note that Asterisk does not attempt to
; validate the parameters or their values, so if you supply an invalid
; parameter you will not know the specific reason it failed without
; checking the kernel message log for the error(s) put there by DAHDI.
;
;echocancel=128,param1=32,param2=0,param3=14
echocancel=128
echocancelwhenbridged=no
; In some cases, the echo canceller doesn't train quickly enough and there
; is echo at the beginning of the call.  Enabling echo training will cause
; DAHDI to briefly mute the channel, send an impulse, and use the impulse
; response to pre-train the echo canceller so it can start out with a much
; closer idea of the actual echo.  Value may be "yes", "no", or a number of
; milliseconds to delay before training (default = 400)
;
; WARNING:  In some cases this option can make echo worse!  If you are
; trying to debug an echo problem, it is worth checking to see if your echo
; is better with the option set to yes or no.  Use whatever setting gives
; the best results.
;
; Note that these parameters do not apply to hardware echo cancellers.
;
;echotraining=yes
;echotraining=800
echotraining=400
rxgain=8.0
txgain=3.0
group=0
callgroup=1
pickupgroup=1
immediate=no
;;;;;;;;;;;;;;;;
; If you are having trouble with DTMF detection, you can relax the DTMF
; detection parameters.  Relaxing them may make the DTMF detector more likely
; to have "talkoff" where DTMF is detected when it shouldn't be.
relaxdtmf=yes
useincommingcalleridonzaptransfer=yes
adsi=yes
sendcalleridafter=2

;;;;;;;;;;;;;;;;
;faxdetect=both
;faxdetect=incoming
;faxdetect=outgoing
;faxdetect=no

;Include setup-pstn configs
#include dahdi-channels.conf

group=1

;Include PBXconfig configs
#include chan_dahdi_additional.conf