This issue can occur if you are running too many FireWire devices -- like a PowerCore, a harddrive and an audio interface -- off of the same FireWire bus. You can try increasing the buffersize / latency for your audio card along with the Buffer Multipliers for the PowerCore in the PowerCore Control Panel (below): For more information about running the PowerCore and audio interfaces on the same bus, please see this answer
Customers with FireWire based PowerCores have reported this type of issue, when using the built-in FireWire connection of this mainboard:
Some chipsets with lower specifications on 3rd party FireWire controllers may also cause the issue. We recommend to use Texas Instruments or VIA chip sets on FireWire controllers for the best performance.