You have not told us how you are attempting to connect the laptop. You would likely use a 1/8 stereo to RCA Wye cable to plug into the CD input jacks. You could also have a 1/8 Wye stereo to 1/4 inch jacks and use two of your input channels. The computer and the mixer need to be powered from the same receptacle. The sound boards in laptops sometimes are noisy. If the above doesn't fix it, buy a computer audio interface such as a UA25EX or others. Some are available for about $70 that use a computer USB port and generate decent clean audio.
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You have not told us how you are attempting to connect the laptop. You would likely use a 1/8 stereo to RCA Wye cable to plug into the CD input jacks. You could also have a 1/8 Wye stereo to 1/4 inch jacks and use two of your input channels. The computer and the mixer need to be powered from the same receptacle. The sound boards in laptops sometimes are noisy. If the above doesn't fix it, buy a computer audio interface such as a UA25EX or others. Some are available for about $70 that use a computer USB port and generate decent clean audio.