I have a weird noise coming from my mixer when I record from the headphone jack of my mixer into the Mic-In jack of my laptop. I will get the sound in a few moments.
Okay, I just (few days) bought a XLR Female to 1/4" Male cord, plugged it into the mic out (which is switched to mic out), plugged it into my computer, and...I'm still getting the weird noise. You can't hear it as much as if it were running through the headphone jack, but it's still there. I have the rest of this post in audio form, if you would care to listen. The audio file has the offending sound and me talking.
Dude! What MIXER do you have? That's not a beeping, it's noise. Give us the whole signal chain. Do you have speakers plugged in somewhere? I suspect so and that's where the noise is coming from. The A-to-D converters built in to computers suck. You need an audio interface to convert audio signal to digital realm. Read the stickies at the top of this forum section for newbies.
That's the kind of noise that's common with built in line inputs or mic inputs.
I don't think there's a fault here. It's just low quality equipment.
You say you think it's the mixer? So take the computer out of the loop and plug the mixer into an amp and speakers, or even just headphones directly.
I bet you don't hear the noise any more.