Hardware

One thing you might do is check out the website of your computer's maker -- some years back I had a Compaq Presario PC that had noisy audio which I assumed was a hardware problem and lived with it. Then one day I was checking for updates and saw a BIOS patch for precisely the noise I was hearing. I downloaded and installed the patch, and the audio noise went away, it had not been a hardware issue, it had been a BIOS bug. I've no idea whether this is the case for you, but it can't hurt to check the vendor site.

Another option you might consider -- at Best Buy or Circuit City or CompUSA or somewhere I saw a little USB dongle that's supposed to do exactly what you want via USB connection. Never tried it myself, all three computers currently being used by this household deliver clean audio out their headphone connections so we just use those. With an external flatpanel and a couple good powered speakers, this laptop makes a dandy way to play DVDs.

Most commonly the cause for hum on an external input is a bad cable. Either end could be bad and cause an open. With noise in one or both channels (right=red left=white) the signal is being inductively induced along with hum. I use a set of the gold tipped mini jack to RCA stereo adapter cables. Any of the Creative sound blaster LIVE cards, depending on what flavor interface (PCI or PCIE) and the depth of your pocket book will usually provide adequate media transfer. I use the soundblaster Audigy Live that's a 24 bit on the PCI card. Pretty good, four channel ouput for surround and works with the top end games and does a good job on getting those LP's on disk.

You most likely have high frequency noise making it's way to the receiver, or a ground loop issue.

If the noise is a low frequency sort of hum, it is a ground loop issue. With power off on both the PC and the stereo, connect a wire from the ground post on the stereo to the case of the PC. The hum should go away.
CAUTION: "IF" the hum is being caused by a wiring problem with your electrical system, connecting a ground wire could damage either or both devices.

Assuming high frequency noise is what you are hearing, the first step would be to get a higher quality cable to run from the PC to the stereo.

Next, try a ferrite bead over the cable at the PC end. You can get these at Radio Shack and some well stocked computer stores.

It would also be worth the time to experiment by routing the cable along different paths at the rear of the PC. Keep the cable as far as possible from mouse, keyboard, USB and printer cables.

It might even help to move the sound card to a different slot. Keeping it as far away from other cards as possible.

As to a different sound card, Take a look at what Turtle Beach has to offer. I am very pleased with my Santa Cruz.

Chas

I agree with Chas here and besides the most likely thing being a Ground Loop which is a common thing with High End HIFI equipment I would also recommend that you try to keep the 3.5 to RCA leads away from the mains power leads as these can induce noise as well.

Generally a Hum is generated because one item isn't earthed properly and the Audio Leads become a default Earth for one of the pieces of equipment which generates a Low Frequency Hum. If you first make sure that you have everything earthed properly and remove any Double Adaptors or unearthed Power Boards this will cure the problem. It also helps to have the Amp & Computer plugged into adjacent sockets on the same Power Board to remove the possibility of an Earth Loop. This should also remove the need to run a common earth between the cases as well.

Just one note of caution here when you run a common Earth you need to make sure that it's actually connected to the metal chassis of the Amp. Some of the Wooden Case Amps don't have a large exposed Metal Chassis to connect directly to and you need to look around for a suitable mounting place for the earth. If you have one of those Plastic Computer Cases the same applies here as well and it would be best to run a lead from one of the Power Supply Screws as that should provide a positive earth.

Col