Hum from headphone jack from T61

[Muse]

Currently I'm using the headphone jack in conjunction with a mini-plug splitter with female L/R RCA connections on the other end and from those a long (25') RCA stereo cord with male RCA's on both ends to send audio to a stereo (mini multifunction stereo) which powers speakers. I play MP3s off the T61 and a LAN connected computer. It was working OK for a few weeks, but now intermittently I get pretty loud hum and I have to jiggle the mini-plug that goes in the T61's headphone jack (twist it back and forth a time or two) to eliminate the hum. Sometimes I have to jiggle the male mini-plug that goes in the headphone jack more than once to make the hum go away. I tried wiping the male mini-plug tip with common pharmacy variety rubbing alcohol but it hasn't eliminated the problem. I suppose a workaround is to buy a USB sound card such as the Behringer UCA202 Audio Interface, like the one I already have (~$30 at Amazon), which is doing service elsewhere in my systems. That would have a USB connection to the T61 and would give me RCA outputs that would presumably be noise free. Is there another (i.e. cheaper) way to resolve this problem?