Humming CV 50s P bass

[Leon Transaxle]

[color=#282828][font=helvetica, arial, sans-serif]Hi,[/font][/color]
[color=#282828][font=helvetica, arial, sans-serif]I have a slight variation on the humming theme here.[/font][/color]
[color=#282828][font=helvetica, arial, sans-serif]I have a CV 50s P Bass and a MIM P Bass Deluxe active.[/font][/color]
[color=#282828][font=helvetica, arial, sans-serif]I have been trying to use them for recording using a Fostex MR8 mkII.[/font][/color]
[color=#282828][font=helvetica, arial, sans-serif]For the last couple of years I have been using the MIM through a Line 6 studio 110 and run the line out of the Lowdown into the XLR of the Fostex which gave a nice quiet transparent recording.[/font][/color]
[color=#282828][font=helvetica, arial, sans-serif]I also recently started using a BDI21 to save getting the Lowdown out of the cupboard. This has resulted in lowish hum which I rectified by keeping in contact with a non-sounding string at all times (so likely to be earthing related) but also a low level high pitched whine on recordings which is removed by applying a low pass filter in Reaper kicking in at around 1k (so not mains hum). So still usable with the above proviso.[/font][/color]

[color=#282828][font=helvetica, arial, sans-serif]Since buying the CV I wanted to use the trebly tapewound sound for recording a couple of songs. Unfortunately there is masses of hiss when it comes to recording. It is not very obvious when playing through the Lowdown (ie playing not recording). There is also an insignificant amount of hiss when playing through headphones into my Korg AX300B. However if I plug the output socket of the Korg into the Fostex (it is the same socket for phones and line out) there is masses of hiss. The same also happens if I plug the BDI21into the Fostex.[/font][/color]
[color=#282828][font=helvetica, arial, sans-serif]I have noticed that touching a metal part of the jack or the Fostex does reduce the hiss a lot. The Fostex does operate with the usual plug in 12v external supply so there is not a connection to earth.[/font][/color]
[color=#282828][font=helvetica, arial, sans-serif]What is the best way forward from this? Does this sound like an earthing issue with the CV? It seems to be earthing through me when I tough the jack so to my mind the CV is earthing to the earth pin of the jack correctly and it is beyond this point that the issue occurs. I have used multiple leads so I think I have ruled that out (unless I have about seven rubbish leads). Surely this can't be an earthing issue with the recorder (as there is no route to earth in the design). I haven't seen it mentioned on the 'net anywhere as a common fault. I also have no real issue regarding hum from any other instrument (OK my Yamaha SSH strat-a-like does hum slightly more but not in an unusable way).[/font][/color]
[color=#282828][font=helvetica, arial, sans-serif]If I need to investigate the CV further where do I need to stick a test meter to check earthing? Obviously the bridge but where else in particular? I would point out at this point I have fitted covers to the CV but the hum seems to be of a similar level with them on or off. I suppose earthing them at the same time while I have them apart wouldn't go amiss (although the HiMass bridge is a tight squeeze under the cover so I think they are touching anyway.[/font][/color]
[color=#282828][font=helvetica, arial, sans-serif]It is also worth mentioning a previous owner has lined the control cavity with copper tape.[/font][/color]
[color=#282828][font=helvetica, arial, sans-serif]Hopefully someone can point me in the right direction as I would like to record using this bass but I want to avoiding annoying the neighbours by resorting to miking up the amp to do so.[/font][/color]
[color=#282828][font=helvetica, arial, sans-serif]Cheers in advance. [/font][/color]