Why does the audio on my iPhone or some songs on my iPhone have static or sound "funny" and distorted?

It first is important to determine whether or not the static or distortion occurs through the speaker(s) or headphones or both.

If static or distortion occurs through the speaker(s) during some phone calls, this generally is related to network conditions and does not reflect a problem with the iPhone itself. If the static or distortion occurs through the speaker(s) while playing some music or video files, the problem likely is with the file itself. If all audio sounds odd through the speaker(s), first try Apple's general recommendations to recharge, restart, update and restore the iPhone. If the problem persists, you may have a hardware problem and need to have the iPhone serviced.

If audio static or distortion occurs through headphones, but not through the speaker(s), it likely means that either the headphones are dying or the audio jack is failing.

First, try using the headphones with another audio source -- like a computer or stereo -- and see if the audio is still problematic. If it still sounds distorted or has static, the headphones should be replaced. If the headphones work properly in another device, then the problem is most likely the audio jack.

Inspect the audio jack and see if it is noticeably cracked or damaged, although it still may need repair even if damage is not visible (it could be a bad solder connection or other internal hardware problem). Try Apple's general recommendations to recharge, restart, update and restore the iPhone as well for good measure.

Also see the below "How do I replace the headphone/audio jack in the iPhone models?"

How do I replace the headphone/audio jack in the iPhone models?

If your iPhone is no longer under its warranty period, Apple can replace a damaged audio jack in the iPhone models for a price that generally is not cost-effective. Specifically, in the US, Apple charges between US$149 and US$269 plus US$6.95 for shipping (as well as applicable sales tax).

Thankfully, however, more affordable third-party repair services are available and self-replacement also is entirely possible for the technically inclined. If you have effectively isolated the audio problems in your iPhone to the audio jack, and you are comfortable performing your own repairs of small electronic devices, iFixit provides instructions for some models. Nevertheless, this repair is difficult and involves many small parts. Consequently, hiring a professional is strongly recommended.

If you are not sure which iPhone you have, each can be identified by unique Model Numbers listed on the back of the phone toward the bottom. For example, the Model Number on the back of the standard iPhone 4S is A1387. From hands-on inspection, EveryiPhone.com diligently has compiled a comprehensive list of model numbers for all of the iPhone models.

From reviewing the instructions, you should be able to determine whether or not you would prefer to replace the audio jack yourself or alternately hire a professional.