Upon close inspection of the track, I found many areas that appeared to have (although small) tire smudges. That is why I thought the intermittent sound drops were random. After I cleaned all the track, the sound only drops at the same spot, on one curve, consistently. The battery must be not taking a charge and therefore the drops. Can't explain the problem on the curve (O-72) as it is totally polished, but thinking the roller might be breaking contact due to unevenness. Off to get a BCR!
Thanks everyone!
Rich