SV8500 - background buzz/hiss on the phones

[phadobas]

So I have been having this buzz/hiss background noise on calls. It only exists on certain types of phone calls. See below:

IP phone <-> IP phone: NO NOISE
IP phone <-> IP PAD card <-> analog phone: NO NOISE
Analog phone <-> Digital trunk card: NO NOISE
IP- phone <-> IP PAD card <-> Digital Trunk card: NOISE!!!

In other words, I get the noise when an IP PAD card AND a digital trunk card (PRI or CCIS) are involved in the phone call. Individually, no problem with the IP PAD cards, and no problem with the trunk cards. Only when the call passes both of them, do I get the noise.

I've checked system grounding and it's fine, but I don't think it could be the cause as the noise is not always present.
I've played around with just about every switch setting combination on the IP PAD cards that has to do with echo cancel and PAD settings (as in volume settings), and also tested switch settings on the trunk cards, but haven't found that right combination. It's not to say that I've tried everything, but based on the manual, I tried those that seem to be the most promising settings.

And then again, the reason could be something completely different.
The system is on S8, with the latest firmware installed on the IP PAD cards.
The system is 7 years old, and you might ask when did the problem start and what changed. Honestly, I don't know when it started. I personally use a softphone, and I don't hear this buzz. So I can't personally tell when it started. For all I know it could have been there since the beginning. Even though it's on all IP phones, only a handful of users are reporting it as a trouble. The first complaint came in about 2 months ago, from employees who are traveling and only using these phones a few times a year. They have not complained about these before. It could be that they never cared or it could be that the noise really just started recently.

Any ideas appreciated.

 

[belevedere]

External interference? Florescent lights? A toy on someones desk?
Clock drift?

 

[phadobas]

CLOCK DRIFT?

What do you mean by that??

(again, noise is only present when both IP PAD card AND a PRI or CCIS cards are involved in the call)

 

[OzzieGeorge]

Clock drift between the isdn card and the exchange can cause noise on ISDN circuits, Where is the clocking derived from? However as the analogues don't get the noise when on an ISDN call, I doubt it will be this.

 

[phadobas]

The SV8500 gets its clocking from a 2400ICS that's sitting right next to it. The 2400ICS gets its clocking from telco, and the 8500 gets its clocking from the ICS, via their CCIS connection.

My vendor has this theory: maybe the buzz is also there on the analog phones, but it's not loud enough to be heard, but for the IP phones, the IP PAD cards may amplify it so you CAN hear it if you listen carefully on the IP phones.

So we MAY have a system-wide issue, and it MAY come from clocking.

If it's clocking issue, and the setup is as above, would there a good way of trouble-shooting this? Or just go blind and test: disconnect clocking from the CCIS and derive clocking from a telco PRI that's connected to the SV8500? And then see what happens?

 

[OzzieGeorge]

It has got to be worth a try, it doesn't cost you anything!

 

[phadobas]

I did it last night. Resulted in no change in the noise.

 

[phadobas]

One of our branch offices is going through a cable migration: IPX->SV9500. They had an extra IP PAD card of the latest version, that comes with an adapted so it fits in the pre-SV9500 PIM/PIR-s. They sent me that card and I installed it and it takes out probably 90% of that noise.

I compared the switch settings of that newer PAD card with mine, and they were exactly the same. But then looking at the manual for the "old" card and the new card, those switched don't exactly mean the same thing. So in essence the two cards were not set up the exact same way. I went ahead and changed the switches on my old card to configure it the same way as the new card was, but it still had the same buzzing sound...

Anyways - I have to return the "new" IPPAD card to our branch office, but it was an interesting experiment. I'll see if my vendor can work out a "fix" or upgrade of my cards.