Loud background noise: cables picking up RF?

You don't have to recognize the sounds for it to be RFI.

True. There are many forms of RFI. But with that said do you think if his problem is RFI, is it being caused from the communication towers?

An arcing from a loose electrical power connection can also create RFI. And in many cases it can be heard in the form of a static sound..

Of course, a whistle can be tube related also.

Also agree.

But, what about the static sound heard 15' away?

When is the noise present? Always ? With or without a signal present ? For all sources ? etc. Does the volume of the noise change with a change in the position of the volume control? The first thing I would do is find out what the noise looks like and what frequencies are present - audible and inaudible. Scope the various points in the signal chain to see where it is present and to see what it looks like. If you don't have a scope - buy one - Kenwood sells fairly inexpensive scopes new and you can probably pick up an old tecktronix cheap. Its not like you'll never have another use for it. You are not hearing transmitted RF through your speakers - you cannot hear RF and your speakers cannot reproduce it - outside the frequency range for both. By seeing what it looks like and where it is you can do more than guess at it.

Is everything plugged into the same electrical outlet? Also look at this - Jensen Transformer - it might be a ground loop and this will eliminate that. Of course it is best not to have anything at all in the signal path but you already have a major problem.

Fully agree with dcstep's recommendations.You have to go for fully balanced system,using shielded and sielded IC..

You might also shield the unused RCA inputs usings specially made plugs{Cardas,Acoustic revive and the likes]

Lastly if you use any type of ionizers make sure they do not fire directly to your preamp input.
good Luck,and dcstep is right on the money

"I get the noise as soon as my preamp and amp are engaged, whether or not I have a source hooked up. Can I buy a cheap AV-style IC from Best Buy and and see if the cables are the problem, or are those low-end IC's they sell really shielded? Are the power cords also a likely culprit?"

In the previous post I did not address this part of your post. The power cords are not the problem. The wire feeding your outlets will still be there and that is not shielded. RFI filters immediately inside your preamp and amp should take care of that anyway unless it is of extremely large magnitude. In which case you may need an external RFI filter. Again - using an oscilloscope to troubleshoot will make life much easier. As to ic's picking it up - maybe. Any shielded IC should work fine. What is important is that the shield is complete and terminated correctly. Make a pair of IC's yourself, terminate the cable so that only one end of the shield will be connected to ground when it is hooked up - make that end the source end in each case. Radio shack best buy or whatever - no need to go to an expensive cable. To minimize any problems as to coverage of the shield (if you are using a mesh vs foil shield)- avoid sharp kinks in the cable. As a quick check- try adjusting the position of the cables that you do have hooked up now. The effectiveness of an antenna for a given signal depends on its orientation - if you start moving the ic's while listening - as if adjusting an antenna - and you hear a change - then yes, your ic's are definitely picking up the interference.