Here are some things to try -
Do you hear any noise from your amp (with normal settings) with nothing plugged in? A tube amp with bad or marginal tubes can inject noise into your chain. Tap the tubes gently with the eraser end of a wooden pencil. If you hear thumps as you tap, you probably have microphonic tubes (tubes with loose elements) - replace them. You can't do much with a noisy solid-state amp (other than ask a repairman to check it), but you can try adjusting the levels of your pedals and amp to see if you can minimize the noise.
Next try plugging your guitar straight into the amp. If you hear noise, try turning your body (and guitar) 90 degrees. If the noise is from an outside source (lights, motors, etc.), the noise will change (get louder or softer). Guitar strings and pickups can act as an antenna for outside noise. Turn off lights, motors, and appliances to see if you can isolate the noise source. Single coil pickups are more susceptible to noise, but humbuckers have a higher output, so both can pick-up noise sources.
Now, try a different cable. Poor shielding and/or loose or dirty connections can cause noise. Found any noise yet?
Start plugging your effects in one at-a-time. Try each effect in bypass and then turn the effect on to see if you can find any noisy pedals. I used to have a Zoom 505 that was noisy all the time (even when off). I replaced the Zoom and still had the problem. I found that the noise was inaudible through amps at the dealer, but could be heard through my Super. If you have one or more noisy pedals, there may be no solution but to replace them. However, you may be able to minimize noise by reducing the gain and rolling off the high-end (treble). Try connecting the effects in a different order. Distortion effects are high gain - they will amplify all noise sources. Place distortions early in the signal chain.
You can reduce the signal gain (including noise) in Fender tube amps with dual inputs by plugging into the 2nd input. Input #2 has an input attenuator and less gain than input #1. You'll have to adjust volume levels in your chain to compensate.
Computer systems also generate a lot of noise. If a computer is nearby - try turning it off.
Let me know how you make out.
[This message has been edited by Jon68 (edited 08-19-2000).]