Pops/clicks on Zap channel resolve after reboot - why?

Every once in a while we will hear pops and clicks on all 4 fxo channels (tdm400) which persist until I reboot the server. The callee does not complain of anything. Simply rebooting the server resolves this completely. Asterisk information does not show pegged memory usage or any obvious problems.

Has anyone else noticed this or figured out why this is happening? I’d like to prevent it in the first place.

Using AAH 2.8 with asterisk 1.2.14, zaptel 1.2.12, freepbx 2.2.0, dell dimension 3000 with pentium 4 2.8 ghz, digium tdm400.

thank you for your thoughts!