Noise on A1200 while incoming call

Hi!

I'm using pair of A1200P cards equipped with FXS modules. The problem appears when some people always speaking, and incoming call rings. All the users in same ring group hears quite loud crackling noise in the handset every time when hanged up phones rings. I think that the problem is in the bad grounding, but the server case is grounded well. Here's a little holes in main A1200 board and a same holes are in modules, looks like here must be some grounding connection between it, am I right? I never found any clues over the web.

Best regards.

Please refer this link:
http://wiki.openvox.cn/index.php/Troubleshooting_of_Analog_cards#Q12.2C_Sound_Quality_Problems_with_Analog_cards

Thanks for link.
Unfortunately, that's not my problem. I'm getting the noise only when other phones ring, and everything is ok in any other cases. No hum or noise from HDs or other stuff, no described IRQ problems. As I understand, the line voltage rises when incoming call comes and phones rings, and it might be cause for that damned noise. Somehow ring signal interferes with already connected lines. Any ideas?

I doubt the noise is because the bad wiring of telephone line. could you try only connect 1 line of a group? in this case the noise should disappear.

another question, is what kind of pc power supply you are using? does it have enough power?

Hi!

Unfortunately, I had no ability to try your your advice yet, but I'll try in several days. The power unit of my PC provides 550 W as listed, for two A1200P boards fully equipped with FXS modules. Is it enough?

So, no one answered my another question: the main A1200 board has small holes under every module, and the modules has the same. Looks like there must be some grounding connection between them, but I never found anything about this in manual. What's the purpose of these holes?

hello:
to make sure the FXS modules and the main module is well connected, the hole is designed to screw on the main board. it is not for ground connection.
regards!
James.zhu