asterisk users - Apr 2008 - Timing issue for Music On Hold - has *anyone* come across this?

Hi there,

We're experiencing the following problem on a handful of boxes and I'm 
wondering if anyone has any pointers for me.

First up, hardware configs on boxes are the same: Dell 860, Dual Core 
Xeon, 1Gb RAM, 2x 160Gb SATA's in Software RAID 1.

Various Trixbox versions - 2.2.3 and 2.4.2 to name two of them.

Problem is that occasionally the music on hold speeds right up - roughly 
2 or 3 times the normal playback speed. Configuration is very simple - 
boxes have Snom SIP phones connected to them and a single SIP trunk to 
SIP provider (which happens to be connected via 100Mb Ethernet, so we 
run G.711 Alaw). Boxes have no hardware, no PRI or PSTN lines into them 
(so therefore no hardware timing source).    zttest displays good 
results all the time (99.97%+).

Reloading Asterisk fixes the problem. Sometimes the problem is back 
within minutes of a reload. Other times, it'll run for ages before it 
happens again...

We've also noticed that a client will report this to us, but when we 
test it it's back to normal without us reloading Asterisk.

Any suggestions on where to look for this would be appreciated. Has 
happened with the default Asterisk MoH files, and also with files we've 
uploaded (in the correct format).

Thanks
Brent