Five possible reasons for this problem which is basically caused by the srings rattling on the frets:
1. You're hitting the strings too hard
2. Your strings are too light a gauge
3. The nut slots are cut too low for those strings (buzz should disappear as soon as you fret the string in this case). Get an expert to fix this problem
4. A fret is too high (buzz disappeatrs after you work up the fingerboard to the offending fret. Again, unless you know what you're doing, take it to an expert.
5. The neck truss rod is too tight and there's a hump in the neck.
6. The bridge saddles are too low for these strings.
Of all of these, the easiest fix is using heavier strings - sounds heaps better too!
Arthur, April 2007