ez, It's normal.
It is normal for the chain to chatter on start up because the oil in the tensioner bleeds off. The new systems hold fluid to avoid this.
You can practically change the rails for what it takes to inspect them. Chains are good for 100,000 miles or more, sometimes a lot more. The rails get brittle with age and if the engine overheats. The chain stretch can be measured and offset keyways installed to correct timing.
I can't imagine why you would have a problem in 20,000 miles.
1985 Mercedes 500SL Euro (Gray market)
1995 BMW 520i Euro (Gray market)
1992 BMW 525it Wagon
1994 Honda Del Sol Si