When I turn on the hot water I start to hear cracking or sort of expansion sounds in a couple of parts of the house. When The hot water is turned off
I still hear some noise. Is it the pipes or could it be the tankless water heater needing to be cleaned?
Probably just the pipes expanding and where they pass through joists or clamps they are tight so the pipes reposition themselves in small increments.
Then the pipes cool down and the process reverses.
When cleaning anything including baby diapers, it is better to sweep off or scrape off as much solid and semisolid material as you can first. (1) Less cleaning fluid or detergent needs to be used, (2) Less of a mushy mess which in turn means that bleaches or disinfectants will be more effective.