I have a 2009 Hyundai Santa Fe (automatic transmission) that makes an odd noise when shifting from 1st to 2nd gear, most often in the first 5-10 minutes after start up. The only description I can really come up with for this noise is a ‘honking’ sound, as if an air horn is being sounded in the distance.
I mentioned this problem when I brought the vehicle in for an oil change at the Hyundai service center, but they said they had never heard of such a thing. My friends have also heard the noise, but no one has any idea what it is. Maybe the sound of the loose marbles in my brain… 
For the time being, be sure that this complaint is properly documented every time that you bring the car to the dealership for service. You have a very long Powertrain Warranty on this car (10 yrs/100k miles??), so even if the transmission fails after the cessation of the warranty, you will be covered for this problem as long as it is properly documented as a chronic complaint. And, of course, be sure that you retain all of the service invoices mentioning this problem.
Thank you for the excellent advice! I took the car into the shop today, so we’ll see what they have to say.
If there is a vacume line going to the transmission, look to see if it is loose.
Thank you, I will offer that suggestion to the Hyundai shop, as they still seem to be shooting in the dark. :",Re: Re: Odd Sound During Gear Shift,
2776892,Trailer brakes won’t do you any good if the tow vehicle frame (or lack thereof) isn’t designed to support the extra weight. You have to follow the owners manual recommendations.,Re: Re: Re: Re: towing a 2500lb pop up camper,
2776930,"I figured as much. I’m gonna buy them locally, probably Town Fair Tire.
Well it turns out that rear wheel splash was loose and vibrating, most noticeably at gear shift. Apparently two washer nuts were missing. To my surprise, this fix seems to have resolved the issue, as I haven’t heard the sound since picking up the car yesterday afternoon.
Thank you for posting a follow up. Normally problems show up here but on one ever tells anyone what the solution was. So thanks.
Yes, I’m the same way, I always want to know how the problem is resolved. This is the first time I have posted on the Car Talk boards, and I appreciate everyone’s comments.