please help with hum/noise in my setup? Driving me nuts

[Joost Assink]

From time to time I experienced a strange problem with my old, simple recording setup. It could only be described as a loud digital rain of noise that would swell up through the monitors and nothing I tried made it go away. It would swell up, fade away some, swell up again, so it's not a constant noise and it could become really loud. It sounded almost like a brazilian 'rain stick' if you know what I mean.

When I completely renewed my setup (2nd new mic, new preamp, new interface, new laptop; only my Rode NT1a stayed) I thought that that problem would be in the past. However, yesterday after recording for a couple of hours, a very low hum started to appear on the recordings which hadn't been there at first. It is not nearly as loud as the other sound I described above, and it sounds very different (the noise had a lot of highs and the hum only lows) but both come and go without notice and swell up and fade away. Nothing I do seems to help (also, there is no indication of why it starts).

If I leave it alone for an hour and startup again, it's gone. What the **** is going on here? Can anyone help me?

[acorec]

It sounds like a feedback problem. If you are using the same power amp, try another one. It sounds like a classic bypass cap going south. The "building up" sound is DC not being blocked as it should. This is just a guess since you said you replaced everything in your sound path. See if this happens with headphones if you cannot test with another power amp.

[Joost Assink]

I'm glad to hear that there may actually be a normal reason for this weird thing. you mean the power amp for monitoring purposes? I had it hooked up to the line out of my sound card and now it's hooked up to the line out of the Tascam US122. Is that what you mean?

If that's what you mean, how come I could record it on the line in?