If the problem occurred immediately after you replaced the carpet and seats, I’d say there’s a very good chance you’ve unclipped a wiring plug or connector to remove the interior, and failed to reconnect it afterwards. A lot of modern cars have airbags in the actual seat (the side airbag usually) and the wiring often runs under the seat.

The best move would be to remove the seats again and check for loose wiring or wiring or connectors that have been damaged of misplaced in the process of the interior’s removal. But before you touch anything under there, disconnect the car’s battery. That ensures you won’t have an accidental airbag deployment that could injure you while you’re working in that space.

If the noise is a metallic rattling noise, then you might be on the right track here. But as well as the timing chain, it could also be the tensioner that keeps that timing chain tight at fault. The fact that the noise goes away after a few seconds suggests that the tensioner, rather than the chain, is at fault. But they could both be worn.

What’s happening is that the tensioner is hydraulically operated and needs engine oil pressure to do its job. When the engine has been sitting overnight, there’s a slight time delay between it starting and enough oil pressure reaching the tensioner to tighten the timing chain and stop the noise. What you’re hearing is the chain flailing around until the tensioner steps up and takes the slack out of it, at which point it stops rattling and goes silent.

Why doesn’t it happen every time you start the engine? Because the tensioner needs time for the oil to drain completely out of it. If the engine has only been stopped a short time, there’s sill enough oil in the tensioner for it to build up pressure quickly and keep things quiet.

Clutch life in most cars is determined by the type of driving you do and the type of driver you are. Cars that do a lot of urban running or towing will almost always have a shorter clutch life. Those used for highway journeys where the gears aren’t being changed as frequently tend to have longer clutch life.

But it’s also true that a driver who is gentle with the clutch and gearshift (as opposed to one who makes fast, hard changes) will also stretch the clutch’s lifespan.

I don’t think 100,000km out of a clutch is any reason to complain and suggests that you’re one of the gentle drivers out there. But before you commit to replacing the clutch, make sure that the slipping is not from poor clutch adjustment or oil on the clutch from a leaking engine seal, rather than a truly worn-out clutch. Of course, even if it is a worn oil seal (the rear-main seal is the most likely culprit) the gearbox and clutch must be removed to fix it, so a new clutch at 100,000km would be a good idea anyway to avoid having to remove all those components later for a clutch change.