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.

This sounds awfully like badly worn transmission. The Dualis in automatic form used what’s called a CVT. Instead of gears inside the transmission, the CVT has pulleys and metal belts that vary their relationship and, therefore, create the various 'gear ratios' the car needs.

When these pulleys and belts wear, they can start to make the noise you’re reporting. And, just like your car, it will get noisier as time passes. Unfortunately, you’re probably looking at a transmission overhaul or rebuild. If you continue to drive it as it is, you’ll almost certainly do more damage, although it sounds like the real damage is already done.

Take the car to a transmission specialist who will be able to accurately diagnose the noise and take it from there.

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.