You have several coaxial issues... Too many splitters with possibly open ports and loose/corroded connectors which are allowing ingress from broadcast TV and especially your 4g phone handsets.
Modem must be on the first 2 way splitter if you've got cable tv service, or no splitter if internet only. All connectors must be shiny and a tad more than finger tight.
I'll bet the outside line is chewed up and waterlogged... Does it run thru trees?
Loss is a little too high for only a 4 way splitter.
If everything is tight, get spectrum out.
break loose and retighten the connectors at the outside grounding block. Or, it could be in the pedestal at the street, or the line could be damaged by the burrowing rodents that gnaw on them
It needs spectrum out.
You did tighten all connectors , correct...? One wall jack could allow ingress in.