Modulating LED bleeds into sound

I made a script that turns on an LED, plays a sound, then dims the LED. The dimming of the LED causes a sound to bleed over into my audio. It only does this when the LED circuit is actively hooked up to the output. If they are disconnected from the output (open pin) the sound does not occur.

I can probably fix it by just turning the LED's off, but I really like them to fade slowly. Any suggestions? Would a capacitor in the LED circuit help? A fallback solution may be to cut off the speaker with a relay as soon as the sound finishes. (timing problem?)

Addendum: OK, so I tried ditching the PWM and just switched the output off. Now I get a speaker pop. Going to try working with the PWM some more, since the modulated hum is less annoying than the speaker pop.. (By the way, I'm using a small amplifier. The noises I'm getting may not be noticeable if the speaker was driven directly off of the project board.)

Sprocketlabs:

It's been a while since we've chatted about this, but we thought we'd follow up. (We sent an e-mail to you a while back about this, too.)

We have a suggestion for your audio pop issue. We noticed that the pop never occurs when we're using a regular, non-powered speaker box, but it can occur when hooked up to an external amplifier (like you're using). However, we only get the pop when we also have an oscilloscope hooked up to the board. What's happening is that there is a mis-match between the Ground of the PCB (supplied though the USB cable) and the Ground of the oscilloscope probe. While this may not be the same as your configuration, we think it's related to grounding. If you power the Fox Board or Project Board from a battery supply or plug in DC power supply, this might help.

Also, you may want to check out our new PWM Audio Jack Board that allows you to hook up Foxonix boards to external speakers or amplifiers. This board has a 3.5mm audio jack, and it scales the output of the Foxonix boards to a level that works for an external amplifier.

We hope this helps!