VR6 Engine Knock

I have a '97 Jetta III VR6 with no other engine trouble or problems. I check fluids regularly, and overall the car runs great. However, when I stop at a stoplight and have the engine idle, the engine knocks every now and then. -Only when it idles. I have no clue on what might be causing this. I've been feeding it higher octane fuel to try and counter the problem, but it's still ongoing. Any help on this would be greatly appreciated.

Alright.. I suppose nobody really knows for sure.. I really thank the people at this forum, it's been great asking for info...

I have a 96 vr6 and i have a similar problem. After i bought the car i heard the noise , but it was too late to return the car. after a few months of worrying, i found out that it is normal for a vr6 engine to knock. The knocking is caused by hydraulic lifters thats why vr6 is different from other engines. You cant get rid of this knock, but i noticed that the noise will slightly decrease if you put a little Lucas oil lubricant and use a 91 octane gasoline. thanx