If you are using the I/O plug for parallel compression, i.e. combining the original kick with the compressed kick, then you may be hearing the effect of uncorrected latency on the compressor I/O.
1. Nominally, the compressor return will be very slightly delayed by the round trip time out of the computer, through the compressor, and back to the computer. Try adjusting for this latency using the free Latency Fixer plugin from Expert Sleepers following the I/O plugin. http://www.expert-sleepers.co.uk/latencyfixer.html
2. Worse than this, you may be experiencing a bug where instantiation of an I/O plugin on an Aux can result in very substantial delays, possibly due to the Aux track failing to be compensated by the PDC. Latency Fixer can help here also, although the settings must be much more extreme. Curiously, a possible fix for this is to add a send to the same bus on another track (or all other tracks?), but leave the send level at -infinity (so no signal is actually being sent). When this works, you are back to situation 1.
Good luck!
Bud