"Straight through" is a very fuzzy word. You claim to have playedyour records 'straight through' your speakers too, and trust me, if it really were "straight through" those speakers wouldn't make a sound.
You have to understand a couple of things about vinyl players: The needle is basically a very small and weak microphone, that instead of picking up the vibrations of the air, picks up the wobbles of the vinyl groove and generates electricity from that.
To make a sound, you need to covert that electricity into vibrations of air, and thats what the speakers do. But when you say that you play your vinyl disks "straight through" your speakers, then this is in fact not straight through at all. If you too the outputs from that needle pickup and put it into a speaker, you would hear nothing. To hear something you must amplify the weak electrical signal so it's strong enough to drive a speaker.
When it comes to vinyl, this is done in three steps.
Step one is to amplify the signal to 'line' levels, which is simply the standard electrical level used between different equiopments such as tape players, and radios and also the level mostly used inside of the equipment.
Step two is to do a RIAA decode on the signal. This is because the signal on vinyl is RIAA encoded, which basically means that they have lowered the bass, so that the grooves can be made narrower. The RIAA decoder amplifies the low frequencies more than the high, so that the signal sounds OK again.
Usually step 1 and step 2 is done simoultaneously in a RIAA preamp.
Step 3 is the power amp, that takes a line level signal and amplifies it so that it can drive a speaker. This is also where you control the volume, by controlling the amount of amplification.
I guess you have an integrated system where the vinylplayer/radio/tape/amp are all in one box, and using the line out and feeding it into the line in of the computer?
In that case, you ARE using a RIAA preamp.
A ground problem is when two different peices of electricity doesn't have the same ground potential. If you don't understand what that means, you need to study some physics.
It's most easily fixed by making sure that all equipment is properly grounded. Many players, even the integrated ones, have ground screws, where you are supposed to connect the grounding. If yours do, put a cable between that one and a metal part of the chassis on your computer.
