[Asterisk-Users] Faint background noise/crackle on FXS port on TDM400P

[Rich Adamson]

> Hi, I have had this issues for ages but have ignored it, but my handsets get  faint background 
crackle on the FXS port. When I connect the
> handset directly into my PSTN, it goes away complete, so I am generating this from somewhere in 
my asterisk box. I get it immediately when the
> phone goes off-hook and it stays through the dialing and call progress.
> 
> I can't think of any other devices generating any interference along the line anywhere between 
the FXS port and my phone handset.
> 
> Any ideas ?

Some things to check........

- put a voltmeter across tip-ring on the phone connected to the TDM card
  to see if the 48 volt DC is varies.
- ensure the 12 volt connector for the card is solidly connected
- check for shared interrupts (TDM card should be on an interrupt by itself;
  hundreds of postings in the archives on how to check, etc.
- call digium support