Fuel pump issues

It could be fuel pump(s) but noisy fuel pump(s) can last a long time before giving up for ghost. I am not sure without checking if your vehicle has either one or two fuel pumps.

Try and identify if it is firstly the fuel pump that is noisy or a noisy valve seal from the fuel accumulator housed close to the fuel pump. Personally, I have never experienced such a fault the fault is academic.

Try out removing your fuel cap and running your vehicle to notice if the noise is affected by this action and check the cap seal condition.

My next suggestions may have no effect but add some relevant fuel cleaner to your tank and run that through the course. Add as well, some upper cylinder lubricant to additionally lubricate the fuel pump bearings if these are the cause but do check if the  lubricant is 'Kat' friendly. 

Depending upon your last fuel filter change, renew this but after running the fuel cleaner through the system so that any bacterial material is collected in your current filter and not clog up you new filter.

Finally, it won't do any harm to start saving up for a new pump(s) and make sure your breakdown cover is up to date.

Although you have mentioned the noise is from under the rear right  passenger seat (assuming viewing vehicle from front, rearwards) a fuel tank breather valve can cause similar noise but that unit is placed by the rear right hand window panel (viewing from rear, forwards).

Do keep us informed. 

That's great news, Thank you for the update.

As far as the diagnostics are concerned; it could be possible, you are right in your thoughts. The diagnostic equipment directs the technician to the area of possible fault, it narrows down the field of diagnosing required BUT, it is up to the integrity of the technician to interpret what the equipment tells him. The machine does not necessarily pinpoint the fault.