It sounds to me like a grounding problem in one of your pieces of equipment but the sound is unusually high pitched for this. It can sometimes come naturally in a guitar when not touching the strings or any metal part, the hiss should disappear when touching almost any metal part of your guitar or amp. Does this only happen when recording? If not:
Does the hissing stop when touching any metal part of the guitar?
Does the hissing stop when touching any metal part of the amp?
Does the hissing stop when touching any metal part of the lead?
The piece of equipment where the hissing doesn't stop touching most of its metal parts may need to be seen by a technician to be fixed.
Check your guitar for bad grounding, either a ground loop or loose wire.
Check your amp for dodgy grounding, either a ground loop or loose wire.
If this is not the problem, it could be a problem of outer emf. This would explain why it only happens at certain times. Is there an electrical thing always turned on when this hissing happens? (Usually high voltage) Try turning all electrical things in your house off (except guitar and amp) including lights and see if the hissing stops. If you are in an apartment, try take your equipment to another persons house and see if the hissing stops. Try to open up the back panel on your guitar, do you see some kind of paint that is around the wood in the electrical section? The paint that may be there is called shielding paint. If this paint isn't there you may have to get a technician to add shielding paint to the insides of your guitar (you could try do this yourself if you want, google shielding paint for guitar).
As a last resort, try to swap around equipment to find the problem. Use a different lead, use a different amp, use a different guitar. If these don't offer a solution, I'm hoping someone with more experience in electronics may know the answer. I know most of this knowledge by the internet, not large amounts of experience so I can't be certain. Try asking on electricalengineering.stackexchange.
Hope this helps. Good Luck. :)