NeedmoreCrunch

Happened to me once, try a different USB port.

Once your POD is plugged into the computer (USB) and is turned on you need to select the pod as a "playback" device in your sound properties. You can do this in your control panel on your computer, or right click the speaker in the system tray and select "Playback devices", select the Line6 POD as the playback device and click the "set default" button then click "ok".

I'm using USB audio on my POD HD Pro w/Windows 8.1 64bit... no problems.

The FV-500H is a mono volume pedal not an expression pedal, there is a difference and that's your problem.

"but the sound is completely different from the settings on the software (mac) than they are on the unit." ??? The physical knobs on the POD do not move when adjustments are made on the POD EDIT software. Looking at the display screen on your POD, navigate your cursor over the amp model in your patch and double-click ENTER. The AMP: EDIT screen shows the knobs and their actual positions regardless of the postion of the physical knob on the front of your POD.

I rolled back the driver to 2.01 and 2.10, there was a mute on the tuner release so it didn't blast the usb driven signal like the current firmware (2.20). But if you turn down the computer sound before using the tuner function, the noise will only be as loud as the computer volume (which is driving the Line6 sound driver). I've found that "ALL THE WAY DOWN" (MUTE) is the best position until this issue is resolved.

I have the same problem when using my POD PRO as a sound card and playing guitar along through a powered speaker. When attempting to activate/deactivate the tuner (whether it's on mute or not) there is a very loud distorted noise, it's much louder when deactivating the tuner. I honestly think I could damage my speaker, it's that loud. I've tried it with the master down, tuner mute... nothing seems to quelch this noise. This is an ongoing issue.