Crackle heard when calling external automated phone system

Crackle heard when calling external automated phone system.

I recently upgraded to Asterisk 1.4.4 and Zaptel 1.4.2.1 and we are configured to use SIP. Most calls I make are fine, but frequently when I call an automated phone system (e.g., my bank), there is a lot of crackling and poping on the line.

Is there a setting that can help with this?

Thanks,

Mark MacVicar