On our Motorhome the grease boot on #8 in the diagram was cracked and dry with no grease when new. Probably due to the fact that the RV was on the lot in the hot Arizona weather for the better part of a year. All the other lubrication points took plenty of grease. If you hear popping and clunking underneath you in the cab then it could be time for a lube job. Metal on metal needs lubrication. I hope this solves your problem.
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