Comes from the old days of the pit, in the north east of england. Miners would say 'wee lad' to the young boys working down the mine. This later, over time, became the unusual word WEELET. (Nothing french about it as one person told me - Oui L'ette - meaning 'Of course!')
or to express great humour/excitement/joy etc.
Just suck it up and shout it loud, make the 'let' part ring out. eg. Weeeleeeeet!