I have two computers, a laptop ( Asus N61j, i7-Q720, 8gb ram) and a desktop (i7-3930k,16g ram etc) on Window 7.
I connected my guitar on Mic input 11 with a guitar simulator turned on,
The thing is, when I don;t play, the noise levels on both computers are different!

my laptop shows -32db -30db (left and right) on the total mix (software playback)
and I see -25db -26db on the desktop!

Every condition was made to be the same before testing(latency settting,Total mix setting, Input level and output level, amp simulator setting).
  and also I felt that on my laptop, the S/N of my old lap top is a little better to my ears !

Do you think it's possible that since the desktop has more USB connectivity and a lot more computer Fans, the noise level actually could be affected?
I couldn;t figure out where the difference is coming from.
Please help me to fix this issue.