Firewire interface noise and a Reaper Q!

It could be a ground loop issue. A quick (temporary only!) test of that would be to use a ground lift on any power cord in your setup that is grounded. If the hum goes away, that's your culprit. A ground lift is nothing more than a 2-prong to 3-prong adapter. If that is the issue, the next place I would look is your service panel. If there is anything else on the circuit (or on the side of the panel itself where the breaker is) like a washing machine, air conditioner, fridge, or something else with a large motor, that could be the source of your issue. One possible remedy would be to rearrange the panel breakers to isolate (as much as possible) your studio from those items. Putting them on the other pole (without overloading that side) would be ideal. Obviously, if you haven't done that sort of work before, I'd consult an electrician. The other option would be to try a good power conditioner (like a Furman). If the power coming into your house is uneven (varying voltage - usually happens in older houses), this could also fix that as well. A good UPS in the mix helps out, too. I used to have this exact same issue with my keyboard live rig (laptop, synths, road rack w/ outboard gear). I ended up just running my laptop on batteries whenever I would play just to eliminate the noise.

Is the noise somewhat high pitched, and modulating randomly? One down side of bus powered audio devices, USB or Firewire, is that fact that it frequently carries RF noise from inside the computer into the the interface. Firewire and USB cables are cheap, and offer poor rejection of these noises. There are ferrite filters that you can attach to the cables...that may help...

what I meant was that it's a bad idea to run without a ground (when it is required). You risk damage to your equipment (and yourself) if there's a power issue. An old house of mine had several outlets that weren't grounded in the basement and one time I was having band practice down there, my guitar player got zapped (really hard) when he touched the strings. I only meant to use a ground lift just to test. See my previous post for fix suggestions. A power conditioner (on all of your gear) could help, but looking in your house's service panel is also a good place to start. Unfortunately, there's really no one step, fool-proof fix. Right now I live in a brand new house and I still had to do some rearranging in my panel when I added a new dedicated 20amp circuit for my home studio gear. And I still get occasional noise depending on what's going on at the time (vacuum, garage door, other things wifey does, etc...). Anything electrical on that same side of the panel could be causing your noise.

Thanks James, a few I had found looked a bit tacky but the Art cleanbox looks a bit more solid! Its a big desktop with a pretty hefty power supply (is that a bad thing when it comes to noise?) Unfortunately the amp just gave in and started crackling so that needs sorting as well, gah!

3 to 2 prong adapter +1