Annoying problem when recording drums. Presonus Firepod!

[Watw-Drums]

Hey so I recently acquired a Power PC iMac G5.

 

I've bought Logic Pro along with it. Now i've recently started recording again with equipment i've used previously on pc's. Same setup, I use a Presonus Firepod patched into a Behringer UB2442FX-Pro mixer.

 

But i've been having some really annoying problems recently when trying to record drums along to guitar tracks and whole songs.

 

But whenever I come back to look at the tracks once i've recorded them, all four tom track's all have a very distinctive humming noise, quite low in pitch. I know this can't be coincidence as it happens at the exact time on all 4 tracks, it's quite prevalent in the track. Now i've tried numerous things, such as plugging the mic's into the firiepod directly, turning the input gain down on the firepod. But one thing that seems to bear the problem is that on the Firpod there is a Knob which distinguishes between the Input's and Playback, when the knob is all the way to the input's it's completely fine, there is absolutely no hum but then when I put it back all the way to playback, you guessed it. The hum returns. Evidently this is a problem seeing as when I turn the knob to input's I can't hear the tracks previously recorded/imported, to play along to.

 

However then if I solo the tracks that are previously imported/recorded and then record the drums, there is a significant difference in the hum volume, to almost the point where it's barely there, but it is.

 

Also another thing i pretty much always have to normalize the track to about 60%.

 

If anyone could shed some light on this i would greatly appreciate it. Cheers

 

Watw Drums