Hi Shaun,
If I unplug USB video DVR A/V just silence, still picking up very low noise plugged in, might be able to improve,
but probably just chips and transistors, no problem with actual sound at the moment....
Looks to me like the USB video DVR is quite sensitive, which is a good thing in some respects.
I will have to find a good quality lead to remove any strain on Pi, or fix it with spacer plugged in direct to match Pi box level.
I'm testing the Pi 3B and 3B+ to the new streamer today (03-06-2018)
https://batc.org.uk/live/gb3gq
The Pi 3B is falling over when presented with fast repeater Rx to Test card switching on poor signals, over a period of time
and does not like weak analog noisy signals.
The Pi 3B+ using the same psu as 3B reading 4.89v on header (reads > 5.1v on 3B ) has not failed to stream, poor inputs as above.
I have a large 5v Psu have to change plug to micro usb, will test on that next, also try to keep the supply a little above 5v as you say.
Both 3B and 3B+ have latest O/S upgrade onboard using same psu and usb dongle.
Looks to me so far that the improvements to 3B+ inc network speed are doing the job.
I have another Pi 3B unpacked to compare...
I have not looked at changing the "yet another de-interlace filter" mods yet....
https://wiki.batc.org.uk/Repeater_Streaming.
Have that on the list.
Quiet streaming test cards, talking heads, shack shots etc outside the Repeater environment the Pi 3B maybe fine...
Apologies for the long post, but giving the streaming / streamer lot's of attention.
Peter
P.S looking at reset and restart options for remote repeater, including last resort removing the power...