Hello,
My '02 Hyundai Sonata has developed a creak. Its coming from under the passenger seat (it’s not coming from the seat itself as the noise is the same whether someone is sitting in the seat or not).
It sounds like an old creaky rocking chair. I hear the sound when I start moving the car or come to a stop or turn the car, or go over any small bump (basically any shift in weight of the car).
The sound goes away after about 20-30 minutes of driving.
I’m not sure what could be wrong, and don’t want to just take it in and let the mechanic have a field day trying to diagnose a random noise.
If it wasn’t so annoying for those first 20-30 minutes… I’d just forget about it. But I am worried that it seems to be so prevalent.
This is likely to be something as simple as a couple of loose bolts on the mountings for the passenger seat.
But, wouldn’t the noise change with a change in weight in the seat? As mentioned… it doesn’t change regardless of whether or not someone is in the seat (or if I jamb my arm against the seat in an attempt to try and pin it up against any loose bolts/screws). Also… if it was just loose bolts in the seat, why would it go away after 20-30 minutes of driving?
Could the noise be coming from beneath the car? If so, then it could be exhaust pipe, but is it more likely the rear rubber bushing on the front right lower control arm. Those can get noisy on many makes and models of car. If that is it, it is annoying but nothing to worry about. Many of them make noise for years when they are not really worn out. Most often noticed in the rainy season.
The way to check is to take some aerosol silicone lubricant and spray the bushing from all angles. If he noise goes away for a while, that was it. You may find that your solution is to hit it with silicone a couple of times a year until the rubber gets a little harder and a little looser and the noise stops.
Yes, it is beneath the car. When I said “under the seat” I meant under the car, directly under the seat… not within the interior cabin of the car (sorry I wasn’t more clear). The exhaust pipe issue sounds plausible… I could see the heat from the exhaust pipe causing expansion and stopping the noise after it gets warm enough (that 20-30 minute time-frame). Maybe a connection point, or an area its rubbing?
I’m not sure about the control arm idea… I would think the noise would be farther forward towards the wheel. It is literally directly in line with the seat though. But as you mention… a couple quick squirts of lube are easy enough to try to eliminate a possibility.
Well, now that you have actually explained the location with some accuracy, you can disregard my suggestion that the noise is coming from the seat mounts.
As usual, the devil is in the details, and also as usual, getting those details is like pulling teeth.
Wow… are the commenters on here always so condescending. Excuse me for not having 100% of the details 100% accurate from the start. That’s why they’re “discussions”… I say something, you ask questions, I respond. It’s called back-and-forth… you might want to try it in the real world… see how it goes for you… 
It is best you figure this out on your own (rather than paying a mechanic) as we mechanics don’t like to get these jobs at all, they never pay the amount of time you have in them. Would you like to work 4hrs and get paid for 1 hr? that is the life of a mechanic when it comes to noises and making it up to you on “the next job” sounds like B.S. from management.