bad rar in every download

It seems that everything I download has atleast one bad rar. I check the download once done with sfv checker, and one comes up bad everytime. If I recheck and download with utorrent, it never fix's it. I always end up having to delete the rar and redownload it.

I have wireless internet if that matters.

May be you have hardware problem - bas sectors on HDD or CRC errors in RAM.
To check your hdd click start menu -> run -> type cmd
In command prompt type chkdsk and press enter
To check your RAM download memtest, burn it to CD and boot your computer with it.