At this point I would clean up around your system, Disconnect everything.
If you have a hardwired mouse and keyboard use them.
Get all sources of RF interfearance out of the room.
Don't even plug in the speakers,, nothing.
Now fire it up and open the software mixer and see if those spikes return.
If they are there , change the audio interface.
If they are not there then you start adding equipment until there return.
This thread is long but did anyone get you to run Latency Monitor?
http://www.resplendence.com/latencymon Back before I had an audio interface I noticed certain PC's or Laptops would show action ( noise floor) if I opened Wave Lab and put it in record standby. This is with nothing plugged in. A PC is potentually a noisey place. USB and Firewire is easily contaminated too.