Hmm... I was just playing a song and I just got the crackling sound again -- I guess I was too quick to say the problem was fixed after a limited amount of listening. However, the crackling/popping is less -- I used to get an average of 3 - 5 per song, and it now occurs only during certain parts of the song and less often. To soon to make that judgement though, I guess. Anyways, I think the problem lies in the old preamp (I am still using the original ones in probably the first batch, as I'm unsure of the model number)? It seems more likely than the amp, since it occurs mainly during the highs.