Mine are in all the way. It's just the same kind of noise that a lot of players make, depending on the DAC they use. It's really not a problem unless you're a complete audiophile, which I'm not (I notice it, but can tolerate it). In fact, I'm not even sure if it's noticeable on low end headphones.
That is the thing, I have pretty nice earbuds, nothing top end, but definitely not the cheapest.
2 pairs of my earbuds have the hissing, the better pair more so.
I have a cheap set of Philips over the ear headphones, no hissing at all on them.
I did have the earbud hissing back on my Droid Incredible, but on my Lumia 900 it is much louder. I did some research today because it was unacceptable for me. This is a common problem among many android phones, as well as iPods and Macbooks.
The problem seems to be more of the Amplifier for the headphone jack than the actual DAC. Note that my Acura TL's ELS system sounds great playing Pandora through MetroRadio on Bluetooth, I'm really impressed compared to my previous phones, I'm also positive that AT&T's 3G/4G help this.
So the fix... Get a headphone amplifier (not really feasible to carry around) or get a headphone attenuator. There are a lot of variables going on here... Mainly from what I understand it is sensitivity of the headphones and impedance. Something to do this is one of the plugs that allows you to adjust the volume of the output sound.
There are a few pricier ones and all of them seem to break, the one I picked up is from Radio Shack:
Gold-Plated Volume Control Cable for Stereo Headphones : Headphones | RadioShack.com
This seemed like magic. My earbuds sound so much clearer, perhaps just because the hiss was so terrible.
Here is one of the forum thread I read:
SR MBP Static Issue: The Problem, Some Facts, and a $14 Fix - MacRumors Forums