Odd noise

does it do this during the summer it might be because it getting cold

Check the oil you might have slung a rod a ride or something I don't know that sounds a little odd usually its just a lifter you mean check the oil if it got any metal flakes in it just like a ride

Check for debris in the engine fan. You may have picked up some trash on the road!

I had a leaf get into my blower motor fan ( It is Autumn) ... drove me nuts until it disintegrated

My 2011 Sonata just started 'rattling' at cold starts. Only lasts about 10 seconds and only in gear. Added washers to upper heat shield with no effect. Had Hyundai look at it and Mr. Tire at oil change. Would really like rattle to go away. Rev engine in neutral and no rattle. Anyone found the source? Appears to be coming from the engine compartment.

"BODY 10-BD-007 OCTOBER, 2010 2011 SONATA 2.4L ENGINE COMPARTMENT RATTLE DURING ACCELERATION - FUEL TUBE HOLDER DESCRIPTION: Some Sonata 2.4L vehicles may exhibit a rattle sound from the driver’s side of the engine compartment, which can be heard from inside the cabin. This can be observed during certain engine operating speed ranges (1600- 2000 RPM) or during light acceleration. The rattle may be caused by the plastic fuel tube holder vibrating slightly against the engine compartment bulkhead. Follow the service procedure outlined in this bulletin to correct the condition by replacing the fuel tube holder with a newly-revised part. APPLICABLE VEHICLES: • Model: 2011 Sonata (YF) equipped with 2.4L engine • Production Date Range: Start of production to August 31, 2010"

Hope that helps!

There is a class action law suit against Hyundai on this. Go to this site and see if your sonata is qualify. https://autoservice.hyundaiusa.com/TXX3/MicroSiteTemplate/MicroSiteTemplateVINValidate/1875