Audio Systems: car audio fault finding, channel amplifier, jimmy hendricks

Question
hey again,
            i havefound out that all the speakers that are connected to my 4 channel amplifier (which are a pair of splits up the front and a pair of 6 inches at the back doors) are all cutting in and cutting back out. they dont completely cut in an dout but just drop off the volume a bit every now and then. when i turn the volume right down i can hear a fuzzy sound coming from the speakers. when the speakers cut out when the volume is on they go a bit fuzzy as well then when it kicks back in it goes back to being perfect. i have tightened all connections at the amp but it still does it. what do u think is wrong with it?

Answer
Hmmm.  That IS a bit odd.  
I need much more information about the problem and your situation to understand what's going on.

-Can you describe what it's like when it cuts out?  Is it like the volume drops down for a few minutes or hours, or is it more like a brief change in sound  as if all the low-frequency thumps are muffled for a second or two?
-Is it only when you've got the thing cranked up or at all volumes?
-Is the fuzzy like sever distortion (like a Jimmy Hendricks guitar sound) or is it just static added to the sound?
-What's the power rating/brand of your amp?
-What kind of car and how old?
-Do you notice anything else frequently? "Service Engine" or "Battery" warning lights?
-Does it only happen or happen more frequently in the summer?  Or maybe (more to the point) when the AC is on?