Lower "Input Z" setting is the solution for FIZZ.
It seems to me that the issue is the difference between a track recorded with
1-guitar > audio interface other than POD >Pod input reamplified >recorded using POD USB verses
2-Guitar>....................>Pod Input >Recorded using USB
This to me indicates that in case/track 1: Using an audio interface to record a direct signal then sending it to the pod isn't sending an identical signal as in track 2. Using the other audio interface is exposing the file to an additional AD/DA conversion which will almost always result in losing a little bit of high frequency. When Re amplifiying this track less fizz will appear due to the high frequency loss from the additional AD/DA conversion.
Solution: there are several options to mitigate undesirable fizz. My favorite is using the POD HD own input Z option. Using lower values instead of auto will do the trick looking at the patches in this thread we see that, as it should be , the noise gate is first in the signal chain which is optimal for most situations, but this creates a problem for the input Z set to "Auto". The input Z setting of auto is following the first effect in the signal chain which is the noise gate so no change is happening as the noise gate has the same input-Z setting for amp without effects. I would use the input Z setting for the tube screamer which is 250K and this will reduce so much of the undesirable high frequencies responsible for most undesirable fizz (There's desirable fizz also and we want to keep that). You can use other values to get the optimal sound and the Input Z setting will make a night and day difference from my experience in many patches where using auto will render the patch otherwise unusable.
Another option would be to put an external physical compressor in front of the pod and that will remove some high frequencies from the guitar signal...
DeanDinosaur thanks for your answer. A true Tube Screamer could serve instead of a compressor?