I was reading a section in my HD owners manual about hydralic lifters. As the book reads: The hydralic lifters are self adjusting. they automatically adjust length to compensate for engine expansion and valve mechanism wear. This keeps the valve mechanism free of lash when the engine is running. When starting an engine which has been turned off even for a few minutes, the valve mechanism may be slightly noisy until the hydralic units completely refill with oil. If at any time, the valve mechanism becomes abnormally noisy, other than a short period immediately after engine has started, it is an indication that one or more of the hydralic units may not be functioning properly. Always check the oil supply in the oil tank first since normal circulation of oil through the engine is necessary for proper operation of the hydralic units. If there is oil in the tank, the units may not be functioning properly because of dirt in the oil supply passages leading to the lifter units. See a HD dealer for services. just thought i'd add it to the mix, it could be what some of the unexplained noises are.